Doug O'Neill, the trainer for Kentucky Derby winner I'll Have Another, keeps an eye on the traffic as he gets ready for the morning workouts at Pimlico on Wednesday. (Jonathan Newton/WASHINGTON POST)

In the heady days since I’ll Have Another won the Kentucky Derby, trainer Doug O’Neill has hung out with basketball stars Kobe Bryant and Pau Gasol, thrown out the first pitch at a Baltimore Orioles game and charmed interviewers with his self-effacing wit.

Thoroughbred racing’s man of the moment, a round-faced 43-year-old with a bartender’s affability and wedding crasher’s love of good times, has proved as comfortable in the spotlight as the chestnut colt who thundered past pacesetter Bodemeister for a 11 / 2-length Derby triumph two weeks ago.

It was an achievement O’Neill had dreamed of since the first time his parents took him to Santa Anita Park, where as a 10-year-old he was awestruck by the crowds, the majesty of the horses and the athleticism of the jockeys. He found his calling.

“I knew it was going to be [horse racing], though I didn’t know exactly to what extent or what I would be doing,” O’Neill said. “But I was on a mission from God to figure out a way to pay the bills doing something related to horse racing.”

The one-time hot-walker and groom seeks the second jewel of the Triple Crown Saturday at Pimlico Race Course, where I’ll Have Another will break from post 9 in a field of 11 horses, Bodemeister among them.

The forecast for the 137th running of the Preakness Stakes calls for clear, sunny skies. But there’s a cloud hanging over O’Neill that could result in a 180-day suspension and $15,000 fine as a result of a failed test for elevated levels of carbon dioxide in one of his horses.

It was O’Neill’s fourth such failed test since 2006, and a ruling could come next week, when the California Horse Racing Board meets behind closed doors (though no penalty would take effect until after June’s Belmont Stakes).

It’s difficult to imagine a more dissonant note — the apparent pattern of rules-breaking clashing sharply with O’Neill’s easy warmth and charisma.

O’Neill has professed his innocence and filed suit over the most recent failed test, which suggests the banned practice known as “milkshaking,” in which a mixture of bicarbonate of soda, sugar and electrolytes are pumped into a horse’s nostrils to delay the sensation of fatigue and, in turn, boost performance down the stretch.

Asked about the potential sanction heading into the Preakness, O’Neill said he would address it more fully after the final leg of the Triple Crown, the Belmont Stakes.

“I owe it to the owners and to the fans and to the horse just to focus in on I’ll Have Another,” O’Neill said following a recent morning workout at Pimlico.

“Milkshaking” — or bicarbonate loading, in more sophisticated terms — gives racehorses an extra buffer against the buildup of lactic acid in the muscles, which causes the sensation of fatigue, according to Rick M. Arthur, equine medical director for the California Horse Racing Board.

It poses little, if any, danger to the horse, Arthur added — assuming the mixture doesn’t seep into a horse’s lungs or isn’t administered in exceedingly high dosages.

But it is banned because it creates an unfair advantage.

“This is really a performance manipulation issue,” Arthur wrote in an e-mail exchange, noting that he was not commenting on O’Neill nor his pending case but rather the practice in general.

Those who know O’Neill find the allegation implausible.

“You really couldn’t think of a nicer person in the world,” says retired history professor Arthur Verge, O’Neill’s mentor at Santa Monica Junior College and father of Mark Verge, recently named Santa Anita’s CEO, who is O’Neill’s best friend. “He was always thinking of other people first. And now he has a vocation he loves, and I think the horses get the idea.”

Adds Jack Sisterson, 27, assistant trainer for the California-based Team O’Neill: “People get jealous — especially in this game. So when you’re at the pinnacle, you’re right at the top, people are always going to try to pull you down.”

There is no hint of anything untoward about I’ll Have Another’s results this year.

The colt has won all three races he has run: The Robert Lewis Stakes, Santa Anita Derby and Kentucky Derby.

“He went through every medication and every physical exam you can think of all three races this year,” O’Neill said. “He’s just an amazing athlete. I think with all the previous stuff, I think I’m going to come out on the good. . . . Hopefully we can kick some butt in the Preakness and kick some butt in the Belmont and after that we can sit down and talk about all that.”

According to Sisterson, a native of England who honed his horsemanship at the equine administration program at Louisville, the potential suspension hasn’t dampened the mood at Team O’Neill.

“To the people who know Doug, there’s not a bad word to say about him,” Sisterson says. “Working for a guy like that makes our jobs easier. I shouldn’t say ‘work’ because it’s not work. We wake up at 4 in the morning, and we’re singing and dancing because we’re going to something we love to do. It’s the way Doug runs his business.”

O’Neill was 10 when his family moved from Michigan to California and made a fast friend in Mark Verge, who shared his birthday and passion for horses. In racing season, they’d cut class at St. Monica’s Catholic School, racing forms in hand, and catch three buses to get to Santa Anita.

Too young to be admitted without a parent, they’d troll the parking lot for an adult willing to pass them off as his own. Invariably the adult would scold them, escort them through the turnstile and then ask whom they liked in the race.

If that failed, O’Neill tried a fake mustache.

“Horse racing was something that we fell in love with immediately,” O’Neill said. “And we’ve never lost the love for the game.”