Three-time Coronation Cup winner St Nicholas Abbey's racing career has been ended by an injury suffered on Tuesday.
The six-year-old sustained the injury at Ballydoyle, the Tipperary base of champion Irish trainer Aidan O'Brien.
Coolmore Racing, which owns the horse - who was favourite for Saturday's King George VI and Queen Elizabeth Stakes at Ascot - hope he can be saved for a stud career.
Vets were attending to the horse on Tuesday morning.
On Derby Day at Epsom in June, St Nicholas Abbey made history as the first horse to win the Coronation Cup three times, having previously taken the race in 2011 and 2012.
He won a total of six Group One races - including at the age of two, four, five and six - and earned close to £5m in career prize money. In total, he won nine of his 21 races.
St Nicholas Abbey claimed the Breeders' Cup Turf in 2011 when the jockey was trainer O'Brien son Joseph, who was 18 at the time and became the youngest winning jockey in the meeting's history.
In March, the horse won the Dubai Sheema Classic at Meydan.