Cox Plate entrant The Gurkha has undergone surgery for an unspecified problem.
Owner Coolmore said on Twitter the dual Group One winner and $13 equal second favourite for the Cox Plate had been taken to hospital on Friday night.
"Classic-winning miler The Gurkha, last seen winning the Sussex (Stakes at Goodwood), has met with a further setback," Coolmore said.
"He was referred to Fethard Equine Hospital and underwent surgery last night.
"He was discharged this morning and is back in his box. Future plans will be announced at a later date."
As well as his Group One successes in the French Guineas and Sussex Stakes, The Gurkha was a close second in both the St James's Palace Stakes and the Coral-Eclipse.