Royal Mo sustained an injury to his right front May 14 at Pimlico Race Course, in his final workout for the Preakness Stakes (G1).
The son of Uncle Mo was pulled up by jockey Gary Stevens approaching the quarter pole while working in company with a local horse. Stevens, who flew in for the work, hopped off just inside the three-sixteenths pole and supported the colt's right front leg as he waited for the equine ambulance to come on the track. Royal Mo was fitted with a splint and led onto the ambulance by trainer John Shirreffs.
He was vanned back to the stakes barn area to be evaluated, and was set to be transported to New Bolton Center near Kennett Square, Pa.
"Nearing the quarter pole, it was going so well, I was starting to think about how much I was going to let him gallop out," said Stevens, who added he heard a loud 'pop' approaching the quarter pole. "He was just pulling me around there having a brilliant work, and before I got onto the turn, that's when I heard it.
"He looked after me and I looked after him."
Royal Mo captured the Robert B. Lewis Stakes (G3) earlier this year for Jerry and Ann Moss, and was coming into the Preakness off a third-place finish in the Santa Anita Derby (G1).
This story will be updated.