The colt will make one final trip to the racetrack for the Belmont Stakes Saturday, but all he will do is lead the horses during the post parade.
"I'm afraid history is going to have to wait for another day," trainer Doug O'Neill said.
Just before dawn I'll Have Another was brought out for a final, light workout.
He looked ready to go for tomorrow's shot at the Triple Crown, but back in the barn, trainers found tendonitis.
It could have taken six months to treat.
"Could he run and compete? Yes," said O'Neill. "But would it be in his best interests? No. We're all a bit shocked but we have to do what's best for the horse and if he can't compete at top level you know he's done enough."
The fear: the injury could have caused him to break down during Saturday's race.
A fall could have been deadly and he still has huge potential value as a stallion.
Still, it was quite the ride starting with the come from behind win at the Kentucky Derby and the powerful finish to take The Preakness.
"It's extremely disappointing and you know I feel so sorry for the whole team," O'Neill said. "We've had such an amazing run."
I'll Have Another started as a scrappy underdog named Cheetos, purchased for just $11,000.
He's now headed for stud duty.