The Olympic swimming star Michael Phelps quickly acknowledged his poor judgment after a photograph showing him inhaling from a marijuana pipe was published Sunday in a British newspaper. Although his admission is unlikely to affect his swimming eligibility, it could affect the millions of dollars he has secured in endorsement deals.

In a statement released Sunday by his marketing agency, Octagon, Phelps, who won a record eight gold medals at the Beijing Olympics, did not challenge the legitimacy of the photograph published by the tabloid News of the World.

“I engaged in behavior which was regrettable and demonstrated bad judgment,” Phelps said. “I’m 23 years old and despite the successes I’ve had in the pool, I acted in a youthful and inappropriate way, not in a manner people have come to expect from me. For this, I am sorry. I promise my fans and the public it will not happen again.”

This is not the first time Phelps has been compelled to issue a public apology for his behavior. In 2004, a few months removed from winning six gold medals and two silvers at the Athens Olympics, Phelps, then 19, pleaded guilty to a drunken driving charge.