Aidan O'Brien has withdrawn his four horses from Sunday's Prix de l'Arc de Triomphe because of concerns over contaminated feed.
The Irish trainer has pulled Mogul, Japan, Serpentine and Sovereign out of the Longchamp feature, where they were due to go up against Enable, as John Gosden's mare bids to win the great race for an unprecedented third time.
None of the quartet will, however, take part after it emerged late on Saturday evening that they have tested positive for a banned substance, believed to be zilpaterol - potentially from batches of feed supplied by Gain Equine Nutrition.
On Friday, the supplier confirmed that it is "investigating the potential presence of a contaminant in some batches of our equine feed range".
O'Brien issued a statement via Ballydoyle Racing's Twitter account on Saturday evening which read: "Unfortunately the results of the urine samples taken from the horses yesterday have come back positive from the French laboratory.
"There is a possibility that the contaminant may have left their system by the time of racing tomorrow however we have no guarantee of this and in order to protect the integrity of racing we have decided to withdraw all our horses from racing tomorrow.
"Joseph and Donnacha O'Brien will do likewise."
O'Brien's two sons each had leading Group One contenders due to race on Sunday.
Donnacha's Fancy Blue was declared in the Prix de l'Opera, while his older brother Joseph had Pretty Gorgeous in the Qatar Prix Marcel Boussac.