A nuclear scan helped doctors diagnose Animal Kingdom with the start of a stress fracture in his hind end.
The injury won't require surgery, and the Kentucky Derby winner could return to full training after 30 days of rest and 60 days of light work.
But his connections also raised the possibility of retirement so that the colt could be put out to stud.
"Team Valor’s interest is to run the horse for another year," Team Valor International CEO Barry Irwin said in a statement. "We will make a decision about whether we want to do that by September, so that if the horse is going to be retired, he’ll have plenty of chance to be promoted by the start of breeding season. [Trainer] Graham Motion and I think we should have a good enough idea by September of whether or not he is the same horse in his training. If he is, we prefer to run him another year and target the Dubai World Cup."
Animal Kingdom, who finished a close second at Preakness, would receive considerable interest from breeders.
The four-year-old has run in only one race since the Belmont, and came up lame the morning after a five furlong training run on Saturday. He required surgery to fix a fracture on the hock of his left hind leg last June, and was kept off the track until winning a claiming race on Feb. 18 in Florida.
The new stress fracture is not related to the previous injury, Dr. Dean Richardson of the New Bolton Center at University of Pennsylvania said.
“If anything was going to happen to this horse," said Richardson, who performed the surgery last June, "this would be about as good a result as one could hope for."
Motion said via Twitter that Animal Kingdom would return to the Fair hill Training Center in Maryland at the end of April.