Leading Australian sprinter Zoustar will not run at Royal Ascot and has been retired to stud after straining a suspensory ligament.
The Chris Waller-trained four-year-old held entries in both the Diamond Jubilee and King's Stand Stakes at the Royal meeting and had already shipped to Britain ahead of next month's feature.
However, he will now return home to Australia to begin his stallion career at Widden Stud, who own the colt in partnership with Qatar Racing and Merrow Racing.
Waller said: "It is extremely disappointing that we are not able to compete at Royal Ascot and the owners and I are devastated by this.
"The horse had travelled extremely well to England and for me personally it was the start of what would have been the experience of a lifetime. To have a horse the calibre of Zoustar to not only race in England but at Royal Ascot would have clearly been a highlight for me.
"A minor problem was detected following his first serious pace work and scans overnight revealed he has a very small strain to a lateral aspect of the proximal suspensory ligament and as a result his work load needs to be reduced as well as being given time off for the area to rest and recover.
"To be informed of the news that Zoustar will not be able to run has been simply shattering as I was confident we had the right horse to do Australia proud. I know myself this horse is the real deal.
"The owners had already planned his retirement this season at Widden Stud due to his stud value where I am sure he will be very popular with breeders."
Zoustar, who has been based with Charlie Hills in Lambourn, bows out as a winner of two Group Ones in Australia but failed to sparkle on his most recent home start in March.
Waller added: "Looking back to his run in the Canterbury Stakes in March where he was clearly below his best, Jim Cassidy reported that the horse was not happy in the ground and changed legs several times and post-race he was mildly lame in behind.
"Looking at it now it could have been a problem that was underlying but with that said wasn't identified in a thorough veterinary examination, including radiograph and nuclear scintigraphy and realistically there was no indication this injury which could have been in its early stages.
"The big positive I can take out of all of this is the fact I have been fortunate enough to be involved with an exceptionally talented racehorse and win two Group One races. His ability, attitude and physical attributes as well as his gentlemanly temperament make him a tremendously special horse to me."