Jockey William Buick is in hospital after his mount Permian died in the Secretariat Stakes at Arlington in the USA.
Buick was unseated as Dante Stakes and Royal Ascot winner Permian, trained by Mark Johnston, broke down after crossing the line in last place.
Assistant trainer Charlie Johnston said Permian suffered a broken leg and was put down.
Buick, 29, was taken to Northwest Community Hospital for treatment.
"I am with William and he is conscious, but complaining of back pain," said Charlie Johnston, who is the trainer's son.
Buick is one of the leading jockeys in Britain, and a retained rider for Sheikh Mohammed's Godolphin team.
Permian won six of his 13 career starts, including when ridden by Buick to victory in the King Edward VII Stakes at Royal Ascot in June.