Michael Phelps has been suspended from swimming for three months after the publication of a picture showing him smoking marijuana, it was announced today.

The Olympian, who won eight gold medals at last year's Beijing Games, issued a public apology after the publication of the photograph earlier this week.

Although he stopped short of admitting to using cannabis, the 23-year-old issued a statement apologising for his “regrettable” behaviour and for having “demonstrated bad judgment”.

Although he has not breached anti-doping rules, the American swimmer's national governing body has imposed a three-month ban and withdrawn financial support as punishment.

A statement read: “This is not a situation where any anti-doping rule was violated, but we decided to send a strong message to Michael because he disappointed so many people, particularly the hundreds of thousands of USA Swimming member kids who look up to him as a role model and a hero.

“Michael has voluntarily accepted this reprimand and has committed to earn back our trust.”

One of Phelps' main sponsors, Kellogg, who signed a lucrative deal with him shortly after his record-breaking success at the Olympics, has decided not to renew his contract which expires at the end of the month, saying his “most recent behaviour is not consistent with the image of Kellogg”.

The suspension runs out in early May meaning he will be eligible for the World Championship trials in July if he decides to defend the seven titles he won in Melbourne in 2007. This year's competition is in Rome in August.

The punishment was announced on the same day the 14-time Olympic champion made his first public comments since the publication of the photograph in a Sunday newspaper.

Phelps, who was sentenced to probation for drink-driving in 2004, told the Baltimore Sun the intense public scrutiny has made him contemplate whether to compete in the 2012 Games in London. “This is a decision of mine that I'm not going to make today and I'm not going to make tomorrow,” said Phelps.

“It's going to require a lot of time and energy and a lot of thinking for myself but also talking to (my coach Bob Bowman) and talking to my family and just deciding what I want to do.”

The photograph shows him smoking a marijuana pipe and is said to have been taken at party at the University of South Carolina in November. Local Sheriff Leon Lott has said he will press charges against Phelps if he can prove he smoked marijuana in his jurisdiction.

Marijuana possession is a misdemeanour in Richland County and is punishable by up to 30 days in jail.