(CNN) -- I'll Have Another, the winner of this year's Kentucky Derby and Preakness Stakes, is out of Saturday's Belmont Stakes because of a leg injury and has been retired from racing, his team said.
Trainer Doug O'Neill said the 3-year-old colt began developing tendonitis in his left foreleg. He called the development "freakish."
"Yesterday, he galloped great, but the afternoon we noticed some loss of definition in his left front leg to which, like every other owner and trainer, we prayed he just kind of hit himself and it was just a little bit of skin irritation.
"We did him up in a special poultice. This morning, he looked great, so I thanked the racing gods there, and we did just a little easy gallop with him today. I thought he looked great on the track, and then cooling out, you could tell that swelling was back and at that back, I didn't feel very good."
O'Neill got a veterinarian to examine the horse, and he determined the injury was "the start of tendonitis in his left front tendon."
O'Neill said the horse could have rested for several months and got started again. But he said I'll Have Another has "done so much that it was unanimous" among the owners and trainers "to retire him."
"It is a bummer," O'Neill said. "Far from tragic, but it is very disappointing."
J. Paul Reddam, the owner, thanked his training team and said, "it was a hell of a run."
"I know they're all personally very disappointed, of course, that he didn't get to show his stuff."
Reddam thought the horse, purchased last year for $35,000, would race and "really show something."
"So we were all a bit shocked, but we have to do what's best for the horse, and if he can't compete at the top level, you know, he's done enough," Reddam said.
The colt and jockey Mario Gutierrez would have made a run for horse racing's first Triple Crown in 34 years. Since 1990, only seven horses have won the first two legs of the title.
Gutierrez and I'll Have Another will lead the post parade for the Belmont Stakes on Saturday, the New York Racing Association said.
I'll Have Another was "lightly raced" and competed in only two prep races leading up to the Derby. He competed in the shadow of Bodemeister, who was predicted to win the Kentucky Derby.
The horse's only disappointing appearance was at Saratoga for the Hopeful Stakes in September.
The Belmont is considered to be the longest and most grueling of the three Triple Crown races. The horses run one complete lap over 1½ miles. The Derby is 1¼ miles, and the Preakness is 1 and 3/16 miles.
The Triple Crown did not acquire its name until Sir Barton won all three races in 1919. Just 11 horses have won the prestigious honor, most recently in 1978, when Affirmed grabbed the title.
Only two other Derby and Preakness winners were unable to run in the final leg of the Triple Crown: Burgoo King in 1932 and Bold Venture in 1936.
Three decades stand out as having multiple Triple Crown winners: the 1930s with three winners, the 1940s with four and the 1970s with three, most notably Secretariat in 1973.
Secretariat also set the world record in 1973, winning the Belmont Stakes by 31 lengths and running the course in 2 minutes, 24 seconds.
Since the 1970s, a few horses have come close to winning the Triple Crown. In 2004, the largest crowd in New York Racing history, 120,139 people, attended the Belmont to see Smarty Jones attempt the 12th Triple Crown win. Smarty Jones finished second.
In 2003, favored Funny Cide finished third in his attempt. Most recently, Big Brown's Triple Crown hopes were dashed in 2008.
The scratch leaves a field of 11 in which Dullahan, the third-place finisher in the Kentucky Derby, is the new morning-line favorite.
Dale Romans, Dullahan's trainer, called the news "devastating."
"I thought it was going to be one of the biggest races in history, and we wanted him to be a part of it," Romans said.
The race will take place at approximately 6:30 p.m. ET at Belmont Park in Elmont, New York.
The time leading up to the Belmont Stakes has not been without controversy. A workers strike at Belmont Park was averted this week.
The racetrack's workers, who manage the grounds and put the horses in the gate, have been involved in a contract dispute with the New York Racing Association over wages and health care since 2010.
I'll Have Another's trainer will begin his 45-day suspension, handed down by the California horse-racing authorities, on July 1.
O'Neill was found responsible for high carbon dioxide levels in 2010 California Del Mar track racer Argenta's blood. However, he was not found guilty of "intentional acts" or any sign that betting was skewed toward Argenta in the race.
Despite that, O'Neill was still able to participate in the Stakes this weekend.
After the news of I'll Have Another's scratch, New York Racing Association Chairman Steven Duncker said he was disappointed for fans and the sport of thoroughbred racing.
"But the most important concern is always the health and well being of the horses. Although there will not be a Triple Crown coronation, we are still looking forward to what will be a terrific day of racing at Belmont Park," he said.
CNN's Ashley Strickland and Richard Roth contributed to this report.