The nine-year-old's final race came last March at Cheltenham
Don Cossack, winner of the 2016 Cheltenham Gold Cup has retired due to injury.
The announcement made on Wednesday morning by trainer Gordon Elliott. "We found that he had a bit of heat in his leg on Monday and we've made the decision to call time", Elliott revealed in a blog for Betfair.
"It's a real sickener for Gigginstown, myself, Bryan Cooper and the whole yard. We knew it was never certain we would get him back to the racecourse and even after that, to get him back to his best, but we were hopeful and he was on track for a run at Gowran Park next month."
The nine-year-old last ran at the Cheltenham Gold Cup last year, where he won comfortably from Djakadam and Don Poli.
Elliott called Don Cossack "the horse of a lifetime", and added he was delighted to see the gelding "retire a champion".
Despite being best known for winning the Cheltenham Gold Cup, Don Cossack also won the Gold Cup at Punchestown and the Champion Chase at Down Royal.
Elliott concluded that Don Cossack "owes us absolutely nothing and a peaceful retirement awaits him out in Gigginstown".
The retirement of the horse means that Thistlecrack's odds have shortened in its bid to win the Gold cup in March.