LEXINGTON, Ky. — A veterinarian says the injury that kept onetime favorite I Want Revenge out of the Kentucky Derby will sideline him for months and could threaten his career if he doesn't respond well to therapy.

Foster Northrop said in an interview Tuesday that swelling in the horse's right front ankle progressed over the weekend, and an ultrasound showed additional ligament damage.

The horse was undergoing a bone scan Tuesday at Rood and Riddle Equine Hospital in Lexington.

Northrop says the prospects of him running again depend on how he responds to therapy over the next two to three months. While the injury is career-threatening, it is not life-threatening, Northrop says.