Aidan O'Brien says it is hard to quantify how huge a blow it is to have withdrawn his four runners from Sunday's Prix de l'Arc de Triomphe due to contaminated feed.
The 50-year-old Irishman said he took the dramatic decision to pull the quartet out late on Saturday after talks with the owners when samples came back positive for a banned substance.
Top English trainer Roger Varian had withdrawn all seven of his runners in England on Saturday due to fears they too had eaten the contaminated feed.
The banned substance is believed to be zilpaterol –- potentially from batches of feed supplied by Gain Equine Nutrition.
"Obviously it is a huge blow," he told English broadcaster ITV on Sunday.
"I cannot really describe it or quantify it.
"Everyone puts so much into it from the owners to the lads and I feel so sorry for everybody really."
O'Brien -- whose best hopes of a third Arc victory lay with Mogul and Epsom Derby winner Serpentine -- said when further results came back positive on Saturday he had conferred with the owners.
They would not have taken the decision lightly -- Serpentine had been supplemented for the race at a cost of 72,000 euros ($84,000) on Wednesday -- as victory in the Arc can add signficantly to a horse's value when they retire to stud.
"The lads (the owners) said there was no choice but to withdraw them to preserve the integrity of the sport," he said.
Gain Time Nutrition had released a statement on Friday saying they were "investigating the potential presence of a contaminant in some batches of our equine feed range".
It is not the first time contaminated feed has played havoc with racing.
In 2002 37 winners were involved when it was discovered morphine had found its way into their feed leading to years of legal wrangles.