LOUISVILLE, KY. -- Medina Spirit's victory in the Kentucky Derby is in serious jeopardy because of a positive post-race drug test, one that prompted Churchill Downs to suspend Hall of Fame trainer Bob Baffert immediately on Sunday in the latest scandal to plague the sport.

Baffert denied all wrongdoing and promised to be fully transparent with the Kentucky Horse Racing Commission during its investigation. Baffert's barn received word Saturday that Medina Spirit had tested positive for an excessive amount of the steroid betamethasone, which is sometimes used to treat pain and inflammation in horses.

Medina Spirit's win over Mandaloun in the Derby stands -- for now.

"To be clear, if the findings are upheld, Medina Spirit's results in the Kentucky Derby will be invalidated and Mandaloun will be declared the winner," Churchill Downs officials said in a statement shortly after Baffert held a hastily planned morning news conference outside his barn to respond to the latest allegation.

The track said that failure to comply with the rules and medication protocols jeopardizes the safety of horses and jockeys, the sport's integrity and the Derby's reputation.

"Churchill Downs will not tolerate it," the statement read. "Given the seriousness of the alleged offence, Churchill Downs will immediately suspend Bob Baffert, the trainer of Medina Spirit, from entering any horses at Churchill Downs Racetrack."

Medina Spirit is expected to run in the Preakness on Saturday, barring some abrupt change in plans or a decision from officials at Pimlico or Maryland's racing commission that would prevent him from entering the second jewel of the Triple Crown.

"I got the biggest gut-punch in racing for something that I didn't do," Baffert said of the failed test. "And it's disturbing. It's an injustice to the horse. ... I don't know what's going on in racing right now, but there's something not right. I don't feel embarrassed. I feel like I was wronged. We're going to do our own investigation. We're going to be transparent with the racing commission, like we've always been.

"He's a great horse. He doesn't deserve this. He ran a gallant race," Baffert added.

The only horse to be disqualified for medication after winning the Derby is Dancer's Image in 1968.

Medina Spirit is Baffert's fifth horse known to have failed a drug test in just over a year. Flanked by his attorney Craig Robertson, Baffert said his barn was told that Medina Spirit was found to have 21 picograms of betamethasone -- slightly more than double what the trainer said was the allowable amount -- in a postrace sample.

Betamethasone is the same drug that was found in the system of Gamine, another Baffert-trained horse who finished third in the Kentucky Oaks last September. Gamine was eventually disqualified from that finish because of that test and Baffert was fined US$1,500. Betamethasone is legal under Kentucky racing rules, though it must be cleared 14 days before a horse races.

"I'm not a conspiracy theorist," Baffert said. "I know everybody is not out to get me, but there's definitely something wrong. Why is it happening to me? You know, there's problems in racing, but it's not Bob Baffert."

Mandaloun, which lost the Derby by a half-length, is not going to the Preakness. If Mandaloun is declared the Kentucky Derby winner, that would mean the Triple Crown pursuit for 2021 would end right there. It is unknown how long Kentucky officials will take to determine whether the results of the Derby should stand or will change.

Baffert was planning to saddle Medina Spirit and Concert Tour in the Preakness, going for a record eighth victory in that race. Except for 2020 when the races were run out of order due to the coronavirus pandemic, Baffert is undefeated with a Derby winner in the Preakness, which holds its post position draw Monday.

Last month, Baffert won an appeals case before the Arkansas Racing Commission after he had been suspended by Oaklawn Park stewards for 15 days for a pair of positive drug tests involving two of his horses that won at the track on May 2, 2020. The horses tested positive for the painkiller lidocaine, which Baffert said they were exposed to inadvertently.

But as Baffert insisted that horse racing can do better preventing doping, he also acknowledged the spotlight.

"I know I'm the most scrutinized trainer and have millions of eyes on me. But you know what? I don't have a problem with that," Baffert said. "The last thing I want to do is do something that would jeopardize the greatest 2 minutes in sports."

The failed drug test is just another in a long series of events shadowing the sport -- and the Derby, its best known and most prestigious race -- in recent years.

Maximum Security crossed the line first in the 2019 Kentucky Derby before being disqualified by Churchill Downs stewards for interference in what was an unprecedented move. Country House, which crossed the line second in that race, is now considered the winner.

In March 2020, Jason Servis -- who was Maximum Security's trainer -- was part of a sweeping indictment that involved trainers, veterinarians and pharmacists in a horse doping ring. Baffert faced the doping allegations in Arkansas and Kentucky last year, and now, this.

"I'm worried about our sport," Baffert said. "Our sport, we've taken a lot of hits as a sport. These are pretty serious accusations here, but we're going to get to the bottom of it and find out. We know we didn't do it."

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AP Sports Writers Tim Reynolds and Stephen Whyno contributed to this report.