Frankie Dettori has lost the ride on Prix de l'Arc de Triomphe winner Treve and will be replaced by Thierry Jarnet in the Prix Vermeille on Sunday, at the request of trainer Criquette Head-Maarek.
Jarnet partnered Treve to her first three victories last season, completing the hat-trick with a brilliant display in the French Oaks, following which she was snapped up by Sheikh Joaan Al Thani's Al Shaqab Racing operation.
After being announced as Sheikh Joaan's retained jockey, Dettori took over in the saddle when Treve landed last year's Prix Vermeille, but after being forced out of the Arc through injury, Jarnet steered her to a memorable victory in October's Longchamp showpiece.
The popular Italian has been back on board this year, with Treve suffering a narrow defeat at the hands of Cirrus Des Aigles on her return to action in the Prix Ganay before returning with pulled muscles after finishing third in the Prince of Wales's Stakes at Royal Ascot.
Head-Maarek feels reuniting the previously successful partnership will have a positive effect this weekend and going forward.
Speaking from Keeneland in America, she told Press Association Sport: "Frankie is not going to ride her in the Vermeille as I have decided Thierry Jarnet will ride. Normally, that means Thierry will ride in the Arc.
"It was my decision, nobody else's. I think it is the best decision for the filly and when I told Frankie he was very good about it and understood my point of view.
"Thierry did very well on the filly last year and there is nothing more to say."
Al Shaqab's racing advisor Harry Herbert stressed the rest of Dettori's retainer was unaffected by the Treve decision.
Herbert said: "These are difficult decisions, but Criquette felt that Thierry Jarnet knows the filly so well on a day-to-day basis and, having won an Arc on her, that for these last two key bullets (Vermeille and Arc) to fire in her career every little percentage shot counts and she wants to give the horse every chance.
"It's obviously very disappointing for Frankie, but he's a phenomenal team player. He's been amazing on this.
"This is not in any way more of an issue than the fact the trainer feels strongly that the filly reacts particularly well to Thierry Jarnet.
"Frankie will be riding Osaila in the Moyglare in Ireland the same day and also riding the others for the Sheikh. It's as simple as that."
Dettori is set to be in action on Tuesday in France, partnering Al Shaqab's 5million guineas purchase Al Naamah in the Prix d'Aumale at Chantilly for Andre Fabre.
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Connections of several contenders in the Ladbrokes St Leger were bidding for Ryan Moore's services with a double-figure field looking almost guaranteed for Saturday's Doncaster Classic.
Khalid Abdullah's two Sir Michael Stoute-trained colts, Snow Sky and Kings Fete, are both set to take their chance and the all-conquering jockey should partner the latter with the owner's retained rider James Doyle expected to discard him in favour of second-favourite Snow Sky.
But Aidan O'Brien admitted Joseph O'Brien will be needed at Leopardstown for the start of Irish Champions Weekend and he has not yet announced a pilot for Granddukeoftuscany.
John Gosden is planning for his trio - Forever Now, Romsdal and Marzocco - to all line up, while Moore has also been offered the potential mount on either Alex My Boy or Somewhat, with Joe Fanning almost certain to be aboard the third of Mark Johnston's contenders, Hartnell.
Stoute won his only Leger back in 2008 with Conduit and Snow Sky trades at 5-1 with the sponsors behind 5-2 favourite Kingston Hill after winning the Gordon Stakes and running second to Postponed in the Great Voltigeur.
Kings Fete, meanwhile, has looked hard to handle when placed in a Goodwood handicap and Listed race.
Teddy Grimthorpe, the owner's racing manager, confirmed both would run.
"Kings Fete worked his way on to the scene on Saturday morning and Michael and the Prince were keen for him to take his chance," he said.
"James Doyle will have the choice, I would imagine he'll go for Snow Sky, it's entirely up to him. I hope an up-and-coming jockey, Ryan Moore, will ride the other."
Johnston has had three thirds from seven previous Leger runners and success for a Yorkshire-based trainer would be popular on Town Moor.
His wife, Deirdre, said: "I think at the moment, if the ground is good, all three are planning to run.
"Hartnell goes on any ground, he'd prefer it slightly softer, and that's the same for Alex My Boy. If it's faster than good, he won't run, and if it's good to soft, or softer, then Somewhat wouldn't run.
"At the moment, Joe has the pick and I think he'll side with Hartnell. We've spoken to Ryan Moore, and we're waiting to see if he will be required by Khalid Abdullah. We have to see what we'll do if all three run."
Four-time winner O'Brien is down to just one probable starter, Voltigeur fifth Granddukeoftuscany.
He said: "Probably only Granddukeoftuscany (will run). Kingfisher will probably go to Leopardstown (Irish Champion Stakes)."
Asked about a jockey, he said: "He has to do a little piece of work tomorrow, and we'll cross that bridge then."
But asked if his son Joseph could make the meeting, he said: "I doubt it, we've a big day at Leopardstown."
Roger Varian was thrilled to see 14mm of rain fall at Doncaster over the weekend, with the course's managing director Mark Spincer reporting the going to be currently good to soft with a favourable forecast for the next few days.
The trainer had to miss the Voltigeur, as his Derby runner-up Kingston Hill does need some give in the ground.
"He's in good form and we're planning to run," said Varian.
"It was great to get a drop of rain as it was a very dry forecast, but at this time of year, with the longer nights and the dew, hopefully the ground will stay there.
"Andrea (Atzeni) will ride, as he has ridden him through all his career."
Gosden, who has had four winners of the race since 1996, was sales shopping at Keeneland but checked into a Leger preview lunch by telephone.
"They're in good order, I was pleased with them on Saturday and it's all systems go," he said.
"I'll talk to William Buick and see which way he wants to go (in terms of riding)."
With 15 horses declared, all the remaining hopefuls in the field are also likely to take their chances.
James Given confirmed Voltigeur third Odeon and Richard Hannon did the same for Gordon runner-up Windshear.
Andrew Balding said he was "hoping Jim Crowley" will ride Scotland, while Marco Botti was pleased to see the rain for Min Alemarat, the mount of Martin Harley.
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Estidhkaar and Richard Pankhurst are two of the star names among 15 juveniles still in contention for the At The Races Champagne Stakes at Doncaster on Saturday.
The Richard Hannon-trained Estidhkaar has not been seen since an ultra-impressive victory in the Superlative Stakes at Newmarket's July meeting and will be a popular choice to follow up on Town Moor.
Hannon could also run Baitha Alga, but he has plenty to prove after finishing tailed off in last month's Gimcrack at York.
Richard Pankhurst has not been seen since streaking clear in the Chesham Stakes at Royal Ascot for John Gosden and has been snapped up to run in the colours of Sheikh Hamdan bin Mohammed Al Maktoum.
There are just two potential Irish challengers, with Aidan O'Brien leaving in The Great War and War Envoy.
Other interesting contenders include Charlie Hills' once-raced Windsor maiden winner Aces, Roger Varian's runaway Denford Stud Stakes victor Belardo and the Barry Hills-trained Nafaqa.
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Al Naamah bids to confirm the big impression she made on her debut and cement her position in next year's 1000 Guineas market when she steps into Group company for the Prix d'Aumale at Chantilly on Tuesday.
The Galileo filly, who cost 5million guineas at Tattersalls Sales last October, returns to the course and distance over which she got off the mark 10 weeks ago. Frankie Dettori takes the ride, taking over from Maxime Guyon.
Harry Herbert, racing advisor for owners Al Shaqab Racing, said of the Andre Fabre-trained youngster: "Her debut race was very good. She has done well physically, as you'd expect her to do.
"She was running early enough for a filly bred the way she is and to win impressively as she did on her debut was pleasing.
"Andre has taken her time with her. She might have gone to Deauville, but he decided not to as the ground was so bad there.
"It was cut up ground, so he identified this race as her next slot, so we'll see.
"She's in good shape. I'm sure whatever happens tomorrow she's got an exciting career ahead of her.
"Let's hope she can win a Group Three on her second start and if she does, she'll be Marcel Boussac-bound (at Longchamp on October 5)."
Among her six rivals is stablemate Shahah, who is in the same ownership.
Freddy Head saddles Clairefontaine scorer Colonialiste, while Mario Hofer's Moonee Valley and the Pascal Bary-trained Night Of Light have won their only starts to date.
Thank You Bye Bye and Kindly Dismiss, who have had plenty of racecourse experience, complete the field.
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Al Kazeem is reportedly in prime condition ahead of the Qipco Irish Champion Stakes at Leopardstown on Saturday.
The six-year-old faces his biggest test in the mile-and-a-quarter Group One since he resumed his racing career following a failed time at stud.
Al Kazeem won the second of his comeback starts at Windsor last month and will now bid to go one better in the Irish Champion than he did 12 months ago, when he was beaten by The Fugue.
Charlton could not be happier with his stable star and is looking forward to have another try at the race.
The Beckhampton trainer tweeted: "Al Kazeem is pleasing me and returns to Group One company in the Irish Champion Stakes on Saturday."
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An additional six Twilight fixtures have been announced by the British Horseracing Authority.
The meetings will be held on Tuesdays at Kempton Park and Wolverhampton from the end of September to early November.
Due to sunset times, only floodlit tracks were invited to apply to stage the fixtures. The HBLB will contribute £2,500 per race in addition to the prize money contributed by each racecourse.
The programme at all fixtures will consist of six races commencing approximately 10 minutes after the last afternoon race.
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Betfred Sprint Cup runner-up Gordon Lord Byron is set to turn out quickly for the Clipper Logistics Boomerang Stakes at Leopardstown on Saturday.
The six-year-old found only G Force too strong when defending his crown on Merseyside last Saturday and trainer Tom Hogan is so delighted with how his stable star has taken those exertions, he is prepared to let him line up on the inaugural Irish Champions Weekend.
Hogan said: "He's actually come home in brilliant form. He had a light canter this morning, he's very fresh and well in himself and it seems as though the race has taken nothing out of him."
He went on: "He left Haydock just after 5pm and by the time he caught his ferry at 8pm he'd eaten up his dinner. When he arrived home at 2am on Sunday he was wondering why he had no food, so the lads gave him another couple of bowls.
"The slow ground probably caught him out on the day and being in front so early took the edge off him as well, but he ran a good race.
"If everything goes OK in the next few days we'll probably let him take his chance in the Boomerang Stakes over a mile in Leopardstown on Saturday.
"If he runs on Saturday it still leaves us three weeks until the Prix de la Foret at Longchamp, which is a nice gap."
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Maarek could bid to bounce back from a disappointing showing in last weekend's Betfred Sprint Cup at Haydock in the Derrinstown Stud Flying Five Stakes at the Curragh on Sunday.
Evanna McCutcheon's stable star was slowly away in the Group One feature on Merseyside and having made his challenge widest of all, he was unable to land a blow as he came home a well-beaten 10th of 17 runners.
McCutcheon is keen to put the race behind her and is willing to let him turn out again on Irish Champions Weekend if underfoot conditions are deemed suitable.
"He's come out of the race well. There's not a mark on him and he's fresh and well," said the trainer.
"The draw was no help to us on the day and he acted up in the stalls, so we'll just put a line through it and move on.
"We wouldn't be averse to running him this weekend if he got his ground. He doesn't need it soft, but we wouldn't want any firm in it."
Maarek's main aim for the season has been to defend his crown in next month's Prix de l'Abbaye at Longchamp and although he has not been in the same form since returning from a summer break, a trip to Paris remains top of the agenda.
McCutcheon said: "We'd ideally like to get another run into him before France, so we'll see what the weather is doing and see how he is in the next few days."
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White Star Line and Carlingford Lough, the first two home in last year's Guinness Kerry National, are among entries 38 entries for this years's renewal at Listowel on September 17.
The John Kiely-trained Carlingford Lough, who has been allotted top weight of 11st 10lb, failed by just five lengths to give White Star Line 17lb last September. The eight-year-old is reported be in good shape after a mid-season break and is an intended starter.
"He has had a good break and if John (Kiely) is happy with him, the plan is that he'll run next week," said Frank Berry, racing manger to owner JP McManus.
McManus has other possible runners in the three-mile handicap chase in the Tom Mullins-trained Alderwood, Lucinda Russell's Tap Night and Jacksonslady from Philip Dempsey's stable.
As well as White Star Line, Dessie Hughes also plans to run Golden Wonder, who was sixth in the Galway Plate.
"They are two fresh horses and this race has been the plan for them for a while," said Hughes.
"Golden Wonder ran a good race in the Galway Plate, but the trip was just a bit short for him and three miles around Listowel should be fine.
"White Star Line won the race last year and he would like a bit of decent ground.
"They are both in good shape."
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Richard Hannon believes soft ground led to Toormore's downfall in the International Topkapi Trophy in Turkey on Sunday.
Last season's champion two-year-old could only finish third, beaten a length by Glory Awaits, at a meeting where the Hannon stable were successful in the International Bosphorus Cup with Pether's Moon.
Hannon has not lost faith in Toormore, owned by Middleham Park Racing and James Pak, and is looking forward to training him next year.
"It was good to see Pether's Moon come back to form when winning the Bosphorus Cup in Turkey," the Herridge trainer told
www.richardhannonracing.co.uk.
"Apart from his hiccup in the Geoffrey Freer Stakes at Newbury last time, he has done nothing wrong this season, and, though he was on and off the bridle, that is him, and, ultimately, he has won easily in the end.
"Like Pether's Moon, Toormore started odds-on for the Group Two Topkapi Trophy out there, and, though he could finish only third, he still picked up £45,000.
"The ground turned very soft and, while Pether's Moon got away with it, Toormore was never happy on the surface, so, under the circumstances, he has run very well.
"He is such a good mover that he wants fast ground, and, while we have not yet decided whether to go again this season, it's good news that he is staying with us as a four-year-old."
The Hannon team also enjoyed a good Saturday with two good juvenile winners in Mutasayyid and Burnt Sugar.
Hannon said: "Mutasayyid won what looked a hot maiden at Ascot and clearly had learned plenty from his debut.
"Frankie (Dettori) liked his attitude, and he is a colt we have always had a lot of time for, so we might now have a look at the Autumn Stakes at Ascot.
"Burnt Sugar emulated his half-brother, Brown Sugar, by winning the Group Three Sirenia Stakes at Kempton.
"We thought that he would enjoy the surface as he won his maiden by six lengths at Lingfield, and he could not have been more impressive.
"Gerald Mosse, who rode Burnt Sugar, was very complimentary and reckons he can continue to climb the ladder, and we might well look for a race in France."