Thoroughbred racing’s 34-year wait for a Triple Crown champion will continue, with the struggling industry’s latest hope for a superstar suffering a fairly common yet career-ending injury Friday.

I’ll Have Another, a gutsy chestnut colt who won the Kentucky Derby and Preakness Stakes with heart-stopping finishes, was scratched on the eve of Saturday’s Belmont Stakes because of a relatively mild case of tendinitis in his left foreleg that could have posed long-term danger if not addressed.

It was a crushing blow for a sport eager to celebrate a feel-good story line it sorely needed. Hit hard by the nation’s economic downturn and struggling to compete with new forms of entertainment and more enticing options for legalized gambling, thoroughbred racing has lost much of the luster it enjoyed when Affirmed last won the Triple Crown in 1978.

“It’s just devastating,” said Dale Romans, trainer of third-place Kentucky Derby finisher Dullahan, who took little joy in his colt being installed as the Belmont’s new favoritefollowing I’ll Have Another’s withdrawal. “It would have been a great race and great for the sport.”

With his furious kick and flair for razor-thin victory margins, I’ll Have Another had the makings of a hero for his time. In an era in which Americans are being asked to do more with less, the 3-year-old did just that, winning the Kentucky Derby with a charge past the favored Bodemeister and replicating his last-second heroics to win the Preakness Stakes by a neck, again at Bodemeister’s expense.

I’ll Have Another lacked the can’t-miss pedigree of Triple Crown champion Secretariat, the so-called Super Horse who was splashed on the covers of Time, Newsweek and Sports Illustrated for his 1973 achievement. Just four months ago, I’ll Have Another was a lightly regarded colt who had been bought for $35,000 and deemed a 43-1 shot in his first race as a 3-year-old.

He didn’t triumph by shattering course records or crushing all comers, as Secretariat had. He won, with jockey Mario Gutierrez aboard, by summoning an extra measure of heart and will to topple one favorite after another — just barely.

All that remained was a victory in Saturday’s grueling 11 / 2-mile Belmont Stakes, in which the colt was installed as a favorite for the first time in his career.

But trainer Doug O’Neill said he noticed swelling in the horse’s left front leg Thursday evening. It subsided overnight but flared up again following a 5:30 a.m. workout Friday. An ultrasound confirmed the early stages of tendinitis.

Given estimates of a three- to six-month recovery, and the possibility that he would suffer flare-ups after returning to competition, O’Neill and I’ll Have Another’s owner Paul Reddam agreed to retire the horse, who will have a lucrative second career at stud. They announced the withdrawal during a news conference beside the Belmont Stakes barn, as I’ll Have Another nibbled on grass, his coat glistening in the sun.

“This is extremely tough for us all,” said O’Neill, 44, dismissing a suggestion that the rigors of the Triple Crown pursuit, which requires thoroughbreds to win three races of different lengths in five weeks, had been to blame.

“It’s just a freakish thing. It’s a bummer, but far from tragic.”

Said Gutierrez, 25, who had ridden I’ll Have Another to his 4-0 record this season: “In the end, everyone is trying to do what is right for the horse. Everybody wanted to see him race. He’ll be my hero forever.”

The build-up to Saturday’s race had been a boon for the sport. A crowd of more than 100,000 was expected at Long Island’s Belmont Park to see if I’ll Have Another could achieve what 11 other winners of both the Derby and the Preakness had failed to do since 1984.

New York’s Long Island Rail Road ramped up train service for Saturday in an effort to keep as many cars off the Cross Island Parkway as possible. Former president Bill Clinton weighed in, picking I’ll Have Another to win. And former jockey Steve Cauthen, who rode Affirmed to glory, openly cheered for I’ll Have Another to break the 34-year Triple Crown drought.

“I think the whole racing world is just dying to have another great horse come along and capture their hearts,” Cauthen told reporters as anticipation grew.

The colt also had a backer in Sally Hill, co-owner of 1977 Triple Crown champion Seattle Slew. “Having a Triple Crown winner would help racing and the interest in racing,” Hill said last month. “It’s not going to solve all our problems by any means, but I think it would be a great help to bring that interest back.”

The first reports of a potential injury to the Triple Crown favorite trickled out around 11 a.m. Friday and were confirmed soon after by O’Neill in a radio interview. Almost immediately the N.Y. Racing Association announced that O’Neill and Reddam would hold a 1 p.m. news conference outside Barn 2, where the 12 Belmont contenders have been sequestered under 24-hour security since Wednesday.

By noon, reporters and photographers sweated and shoved 10- and 12-deep behind a picket-fence partition, jockeying for position as a news helicopter whirred overhead.

By 12:45 the crowd had doubled, and a section of the picket fence collapsed. The proceedings reached the height of absurdity when a track official stepped to the microphone shortly before Reddam and O’Neill appeared to plea for journalists to “keep the noise down” for fear of disturbing the already agitated Belmont contenders, neighing and whinnying in the stables just 10 feet away.

Larry Bramlage, an equine orthopedic surgeon who was briefed on the diagnosis by I’ll Have Another’s veterinarian, characterized the injury as “a well-known occupational hazard of race horses” — much like a sprained ankle among basketball players.

“It’s a very minor injury, but it’s significant in that it tends to progress if you race on the injury,” Bramlage explained. “And it’s a slow-healing injury, so it takes awhile to rehabilitate.”

If I’ll Have Another were a gelding, Bramlage said, he likely would race Saturday. But because I’ll Have Another has a breeding career ahead, Bramlage conceded it made business sense to retire him now.

That decision, of course, deprives fans who had just begun to embrace the sport’s plucky new star from seeing him compete again.

I’ll Have Another is just the third winner of both the Derby and the Preakness unable to run in the third and final leg of the Triple Crown (along with Burgoo King in 1932 and Bold Venture in 1936). Jockey Kent Desormeaux intentionally eased off Triple Crown contender Big Brown in the late stages of the 2008 Belmont when he sensed the horse, who had suffered a cracked hoof shortly after winning the Preakness, wasn’t on sound footing.

In a ceremonial tribute, I’ll Have Another will lead the post parade for Saturday’s race.