Muth, the likely Preakness Stakes favourite, will not be competing on Saturday because of a fever spike that occurred while arriving at Pimlico.
As a two-year-old, Bob Baffert's son of Good Magic was gaining popularity, and after winning the American Pharoah Stakes at Santa Anita, he was back at the California track to compete in the Breeders' Cup Juvenile.
Although he was only able to come second that time, he hasn't lost since the beginning of the year and easily won the Arkansas Derby in March after winning the San Vicente Stakes.
When Muth scored at Oaklawn Park, he had Kentucky Derby star Mystik Dan in third place. His team was looking forward to facing the Churchill Downs winner in the second leg of America's Triple Crown.
But Baffert admitted that once Muth's temperature soared to 103, he was forced to shave.
“We are sick about this. The horse had been doing really well,” Baffert told the Pimlico media office. “But we have to do what’s right by the horse.”
Baffert now has only Imagination remaining in the Grade One race, with Frankie Dettori's first Preakness ride likely to come from the Santa Anita Derby runner-up.