The 2,000 Guineas runner-up Wichita has died after suffering complications following an injury in Australia earlier this month.
In a statement, Racing Victoria said the horse was "humanely euthanised".
The Aidan O'Brien-trained horse injured his right hind leg during track work at Werribee near Melbourne on 14 October and required surgery.
But while rehabilitating, the three-year-old sustained a further injury to the same leg.
Wichita had an impressive juvenile career before finishing second behind Kameko in the first Classic of the delayed 2020 Flat season.
His last run saw him win the Park Stakes at Doncaster in September under Frankie Dettori.