So You Think has been retired after he was ruled out of the Coral-Eclipse Stakes at Sandown on Saturday.
The 2011 winner, trained by Aidan O'Brien, was found to be lame in his stable on Thursday.
It was due to be So You Think's final run before a breeding career in his native Australia.
The trainer's wife Anne-Marie said on Twitter: "So You Think was found to be lame in his stable a short time ago and will not run in the Eclipse."
So You Think, who beat Workforce in a thrilling finish to win the Coral-Eclipse last year, had been in outstanding form this season.
He won the Tattersalls Gold Cup at the Curragh and then denied the Queen's horse Carlton House to win the Prince of Wales's Stakes at Royal Ascot.
Saturday's Coral-Eclipse, which has attracted 10 runners, sees the return to the track of Dante Stakes scorer Bonfire, who was disappointing in the Epsom Derby, and Godolphin's Dubai World Cup winner Monterosso.