Kentucky Derby winner Medina Spirit collapsed and died after a workout Monday at the Santa Anita racetrack in California.
The 3-year-old colt trained by Bob Baffert had just completed five furlongs in his second workout since finishing second in the Breeders' Cup Classic a month ago at Del Mar, according to Craig Robertson, Baffert's attorney.
Santa Anita spokesman Mike Willman also confirmed the colt's death.
The colt will undergo a full necropsy, which is required by the California Horse Racing Board.
Medina Spirit tested positive after the May 1 Derby for betamethasone, a legal medication that is not allowed on race day. It was Baffert's record seventh win in the Derby.
Last Friday, Robertson released a statement saying that tests done by a New York lab have "definitely confirmed" Medina Spirit tested positive for the steroid — not through an injection but due to an ointment used to treat a skin rash.
The Kentucky Horse Racing Commission has been investigating the case, and has yet to hold a hearing that could possibly disqualify Medina Spirit.
In the $6 million BC Classic, Medina Spirit couldn't muster the necessary late kick to threaten winner Knicks Go.
"I'm very proud of him. He ran a great race," Baffert said last month. "To me, he's the best 3-year-old. He showed it today. That's what racing is all about, proving it on the racetrack. And he proved it today that he's the real deal."
Baffert was allowed to enter horses in the season-ending world championships, but the event's money-leading trainer had to meet certain conditions, including stricter out-of-competition testing of his horses and greater security at his barn. He agreed to the extra scrutiny and was required to pay for it out of his own pocket.
Medina Spirit had five wins in 10 career starts and earnings of $3,545,200, according to Equibase. The colt was owned by Amr Zedan, who competes as Zedan Racing Stables.
Additional reporting by The Associated Press.