Kentucky Derby winner Medina Spirit has tested positive for a banned substance, trainer Bob Baffert said Sunday, and the horse could be stripped of its history-making victory.

Baffert told reporters at a Sunday news conference at Churchill Downs in Louisville, Kentucky, that post-race testing showed Medina Spirit was positive for 21 picograms of betamethasone, an anti-inflammatory steroid medication not allowed to be used within 14 days of competition.

Baffert denied treating the colt with the medication and said he will investigate the test result to determine how the substance got into the horse's system following the race.

"I got the biggest gut punch in racing for something I didn't do," said Baffert, who claimed a record seventh Kentucky Derby victory with Medina Spirit but who is now again under scrutiny after this latest in a string of drug test failures.

"It's disturbing," Baffert said. "It's a complete injustice to the horse."

Churchill Downs announced Sunday it has banned Baffert from entering any horses at the racetrack while it awaits the conclusion of an investigation by the Kentucky Horse Racing Commission.

It would take a second positive result from a split sample for the horse to be disqualified.

Medina Spirit ridden by jockey John Velazquez could be stripped of the  Kentucky Derby victory
Medina Spirit ridden by jockey John Velazquez could be stripped of the Kentucky Derby victory GETTY IMAGES NORTH AMERICA / Tim Nwachukwu

But if the second sample does come back positive Medina Spirit's results would be invalidated and runner-up Mandaloun will be declared the winner, Churchill Downs officials said.

"Failure to comply with the rules and medication protocols jeopardizes the safety of the horses and jockeys, the integrity of our sport and the reputation of the Kentucky Derby and all who participate. Churchill Downs will not tolerate it," the racetrack said in a statement.

"Given the seriousness of the alleged offense, Churchill Downs will immediately suspend Bob Baffert, the trainer of Medina Spirit, from entering any horses at Churchill Downs Racetrack.

"We will await the conclusion of the Kentucky Horse Racing Commission's investigation before taking further steps."

But critics were already piling on the three-year-old colt and his trainer, former US President Donald Trump saying, "So now even our Kentucky Derby winner, Medina Spirit, is a junky... the whole world is laughing at us."

Baffert wasn't laughing, however, vowing to challenge the finding as far as he could.

"I'm going to fight it tooth and nail," Baffert said. "I owe it to the horse, I owe it to the owner and I owe it to our industry. Our industry needs to step up and we need to do a better job in racing."

Medina Spirit trainer Bob Baffert raised the winner's trophy after the 147th Kentucky Derby but the result could invalidated after the horse tested positive for a banned substance in post-race sample
Medina Spirit trainer Bob Baffert raised the winner's trophy after the 147th Kentucky Derby but the result could invalidated after the horse tested positive for a banned substance in post-race sample GETTY IMAGES NORTH AMERICA / ANDY LYONS

"I don't feel embarrassed," Baffert said. "I feel like I was wronged.

"There's problems in racing, but it's not Bob Baffert."

Baffert set a record for the most wins by any trainer in the Derby's 147-race history on May 1 when 12-1 Medina Spirit won under jockey John Velazquez to give Baffert his seventh career Derby title.

Two of his Kentucky Derby winners, Justify and American Pharoah, went on to claim the Triple Crown with wins in the Preakness and Belmont Stakes.

Not only might that title be stripped, Medina Spirit might not be allowed to race at the Preakness.

The Maryland Jockey Club, which operates the Preakness and host track Pimlico, said it will review "the relevant facts" before deciding on Medina Spirit's status for the race.

"We are committed to achieving the highest level of horse care and safety standards, and we have a proven track record of pushing those standards forward," the club said in a statement.

In addition to having a blood sample taken upon arrival in Maryland, Medina Spirit would be drug tested if he finishes in the top three in the Preakness.

Betamethasone in a race-day sample would also be considered a positive test in Maryland.

Apart from last year, when the three races were conducted out of their usual order due to the Covid-19 pandemic, Baffert's Derby winners are unbeaten in Preakness runs.

The New York Times reported last November that Baffert-trained horses had failed at least 29 drug tests over his career.

Among them was Justify, the 2018 Triple Crown winner who tested positive for an anti-nausea drug in his final Derby tuneup, a violation not revealed until after the coveted treble was complete.

Baffert blamed environmental contamination and California officials ultimately upheld Justify as the 2018 Santa Anita Derby winner.

Last month, Baffert won an appeal of a 15-day suspension by the Arkansas Racing Commission after two winning horses tested positive for a painkiller in May of last year.