Aidan O’Brien has withdrawn all four of his horses from Sunday’s Prix de l’Arc de Triomphe in Paris after they tested positive for a banned substance.
It is suspected that the prohibited substance was in contaminated feed.
The Irish trainer was due to run Mogul, Japan, Serpentine and Sovereign in Europe’s richest race, which Enable is bidding to win for a record third time.
His sons Joseph and Donnacha have also withdrawn horses they were due to run in other races at the meeting.
A total of 11 horses trained by the trio will be absent.
“Unfortunately the results of the urine samples taken from the horses have come back positive from the French laboratory,” said a statement from O’Brien’s Ballydoyle Racing base.
“There is a possibility that the contaminant may have left their system by the time of racing on Sunday, however we have no guarantee of this.
“In order to protect the integrity of racing we have decided to withdraw all our horses from racing (on Sunday).
“Joseph and Donnacha O’Brien will do likewise.”
On Friday night the ability of Aidan O’Brien’s runners to run at the ParisLongchamp fixture was thrown into doubt.
France Galop announced five horses had tested positive for the prohibited substance Zilpaterol, which was suspected to have been in contaminated animal feed.
O’Brien’s two runners in France on Saturday were given the go-ahead to race after urine samples sent to the Irish Equine Centre came back clear.
But his contenders for the Arc had yet to be given the go-ahead, and the withdrawals will cast a cloud over a hugely-anticipated fixture.
Aidan O’Brien’s leading Arc contender, Love, was pulled out earlier in the week after heavy rain left the official going as very soft.
The absence of his quartet leaves Enable, the mount of Frankie Dettori for British trainer John Gosden, facing 10 rivals – with the field reduced from 15 to 11.
Aidan has also taken St Mark’s Basilica out of the Prix Jean-Luc Lagardere as horses trained by the O’Brien family were withdrawn from a total of three other Group One races.
Joseph was due to saddle leading contender Pretty Gorgeous in the Prix Marcel Boussac, while Fancy Blue will miss the Prix de l’Opera for Donnacha.