Improbable will have Triple Crown-winning jockey Mike Smith aboard if the colt runs in the Preakness on May 18.
Trainer Bob Baffert said Wednesday that he was making the switch from Irad Ortiz Jr. because "Mike and I have a little luck together."
Baffert and Smith teamed with Justify to win the Triple Crown last year.
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Ortiz rode Improbable to a fifth-place finish in the Kentucky Derby on Saturday and the colt was moved up to fourth following Maximum Security's disqualification for interference.
Baffert said Improbable will train Monday at Churchill Downs, and then he will make a final decision on the colt's status for the Preakness, a race the trainer has won seven times. If Improbable joins the field for the middle leg of the Triple Crown, he would arrive in Baltimore three days ahead of the race.
The rest of the maximum 14-horse field for the Preakness has begun taking shape. Neither Maximum Security nor Derby winner Country House will run it.
War of Will, squeezed when Maximum Security drifted out at the Derby as the leaders were coming out of the final turn, was back training Wednesday. The colt had his right front shoe removed and his foot soaked in Epsom salts after experiencing discomfort, trainer Mark Casse said.
War of Will finished eighth — 4½ lengths behind the first-place finisher — and was moved up to seventh via the DQ.
Trainer Mike Trombetta said he will decide by Friday whether Win Win Win runs in the 1 3/16-mile race. The colt ended up ninth in the Derby and emerged unscathed from the race, which was run on a sloppy track for the second straight year.
Also under consideration is Bodexpress, moved up to 13th after finishing 14th in the Derby. The colt is 0 for 6 in his career.
Among fresh prospects are Bourbon War, who would be ridden by Ortiz, Alwaysmining, Anothertwistafate, Laughing Fox, Owendale and Signalman.