Crystal Ocean has suffered a career-ending injury on the Newmarket gallops.
The incident occurred as the Sir Michael Stoute-trained five-year-old, who won June's Prince of Wales's Stakes at Ascot under Frankie Dettori, took part in a routine canter on Thursday.
Crystal Ocean was never out of the top three in a 17-race career and lost to Enable in an epic King George VI & Queen Elizabeth Stakes in July.
"The hope is he makes a full recovery," said a spokesman for the owner.
"He's had to have two screws inserted into a cannon bone.
"At this stage the vet sees no problem at all in him heading to stud, but it is early days. "