I’ll Have Another has been retired due to a tendon injury on the eve of his bid for the US Triple Crown.

The colt was found to have a swollen tendon on Friday, the day before the Belmont Stakes in New York.

“It’s a bummer. It’s not tragic, but it’s a huge disappointment,” trainer Doug O’Neill said.

I’ll Have Another, who won the Kentucky Derby and the Preakness Stakes in stirring style, was the 4-5 favourite to win the Belmont and become the 12th Triple Crown winner and first since 1978.

“Could he run and compete? Yes. Would it be in his best interest? No,” O’Neill said.

He said the swollen left front tendon was the beginning of tendinitis which could have taken six months to treat, and the decision was made to end the colt’s career.

“Yesterday he galloped great, but in the afternoon we noticed some loss of definition in his left front leg,” O’Neill said.

“We did just an easy gallop today. I thought he looked great on the track, and then cooling out, you could tell the swelling was back.”

The trainer said he conferred with owner J Paul Reddam and they contacted Dr Jim Hunt who examined the horse.

“Dr Hunt scanned him and he said it was the start of tendinitis in his left front tendon and you can give him three to six months and start back with him,” O’Neill said.

“It was unanimous between the Reddams and my brother and I and everyone at the barn to retire him.”

Reddam said it was in the best interests of the horse to be retired.

“We’re all a bit shocked, but we have to do what’s best for the horse,” he said.

“And if he can’t compete at the top level, he’s done enough.”