Trainer Bob Baffert, who won a record-setting seventh Kentucky Derby with Medina Spirit this month, on Sunday said the dark bay colt had failed a drugs test.
Baffert said a post-race sample provided by Medina Spirit had tested positive for 21 picograms of the anti-inflammatory drug betamethasone, over the legal limit in Kentucky racing.
Medina Spirit, ridden by jockey John Velazquez had secured a half-length victory in the 19-horse Kentucky Derby on May 1.
Baffert's camp were informed of the news by Kentucky officials on Saturday, but the 68-year-old denied giving the horse illegal substances and said the positive test was "the biggest gut punch in racing".
"I was totally shocked when I heard this news," Baffert told a news conference. "I'm still trying to absorb it. I am the most scrutinised trainer. The last thing I want to do is something that would jeopardize the greatest sport.
"This shouldn't have happened. There's a problem somewhere. It didn't come from us. It's such an injustice to the horse. I don't feel embarrassed, I feel like I was wronged."
Last month, Baffert successfully appealed against a 15-day suspension given to him by the Arkansas Racing Commission after two of his horses had tested positive for a banned substance.
Baffert said Medina Spirit had not yet been officially disqualified from the Derby and that he would launch his own investigation.
"I'm going to fight it," he added. "There are problems in racing, but it's not Bob Baffert. I don't believe in conspiracy theories, but why is it happening to me"
In 2015, Baffert-trained American Pharoah became the first horse since 1978 to win U.S. thoroughbred racing's coveted Triple Crown. Baffert celebrated another Triple Crown in 2018 with Justify.
(Reporting by Arvind Sriram in Bengaluru Editing by Toby Davis) ((Arvind.Sriram@thomsonreuters.com;))