According to reports on Horse Racing TV (HRTV), it appears that I’ll Have Another has suffered a tendon injury that will not only prevent him from running in the Belmont Stakes but will also likely end his racing career.
A tendon injury is typically not life-threatening, but it is a serious injury and the recovery time can be a minimum of three months or longer. Additionally, due to the importance of the legs of a horse, and the fact that re-injury to a tendon is difficult to correct, top class horses are generally retired even after they have recovered from the initial injury.
A greater explanation of the importance of a horse’s tendon is detailed at the website For The Love of The Horse:
When horses move, their tendons must be flexible enough to stretch and contract within a range of 1 to 3 inches. If a tendon is pushed beyond this linear "stress capacity," tendon injury is likely to occur. Such damage to the tendon usually involves rupture of the tendon fibers. The number of ruptured fibers is directly related to the seriousness of the injury.
With the statement by trainer Doug O’Neill that I’ll Have Another has likely run his last race, it appears that he has suffered a serious injury to the tendon.