It had started with a gleeful release from the stress of being the world's greatest Olympian. A student party, a few drinks ... and then Michael Phelps was captured, like so many other errant sportsmen, by someone using the camera on their mobile phone, making his fateful mistake. In the space of a week, Phelps the Olympian, who went home from Beijing the hero with his record haul of eight gold medals, had become the Olympic-size dope caught appearing to smoke cannabis, banned from the sport he loves and potentially facing criminal charges.

Curiously, just a day after Andy Murray and Rafael Nadal, two of the world's leading tennis players, claimed that they were being hounded by the anti-doping authorities, Phelps provides the greatest evidence that, no matter the inconvenience, being shown to be clean is as important as a sportsman knowing he is clean.

Phelps was caught out of competition and before the introduction of the strict regime that worries Murray, which demands that athletes are able to present themselves for a drugs test for an hour of every day in the year. Phelps was on a rare day off, but it hardly matters now, trapped as he was by his own foolishness.

If only he was as wise out of the swimming pool as he is fast in it. It hardly takes a genius to understand that the most high-profile athlete in American sport will be watched by chancers everywhere looking to make a fast buck out of the slightest indiscretion. Whoever it was who had the camera to hand to snap Phelps apparently smoking marijuana through a glass pipe, somewhat unfortunately called a bong, made a few quid, but, in those few seconds, Phelps lost his reputation, his aura and, possibly, tens of millions of dollars in earnings from sponsors.

World in Motion: fighting on ice

Owen Slot considers the end of hockey brawls, David Beckham's waning popularity (in New Zealand) and dope-smoking sumos

• World in motion: best rugby interviewees, Ronaldo's regime, cannabis and porn

• World in Motion: Thorpedo’s sexuality a talking point again

• World in Motion: Andy Murray's less than prodigious effort

Simon Barnes: My perfect weekend . . .

The Times columnist is hoping that the battered England team can produce coherence and that Wigan Warriors can triumph

• Simon Barnes: My perfect weekend

• Simon Barnes: My perfect weekend

60-second interview: Daryl Harper

The Australian, third umpire for the Test in Jamaica, talks about banter and the aftermath of the Mumbai terror attacks

• 60-second interview: Simon Jordan

• 60-second interview: Peter Ridsdale

Superstitions: Delon Armitage

The England full back talks about his problems with nerves before a big match and how he learnt to motivate himself

• Superstitions: Jeff Reed, Pittsburgh Steelers kicker

• Superstitions: Bob Willis, former cricketer

Related Links

• Drugs claim could spell disaster for Phelps

• Michael Phelps: touching history

• Michael Phelps: adapting to life on land

Kellogg's, which had put Phelps's beaming smile on its cereal packets, was first to throw him over the side. But then, millions of kids tucking into their cornflakes, poured from a packet adorned by the image of a man who gets his energy from a bong, was never going to be the best marketing fit.

“Michael's most recent behaviour is not consistent with the image of Kellogg,” the company simply said yesterday, after not renewing his $1million (about £680,000) contract due for renegotiation this month.

So far, his other key sponsors - including Omega watches and Speedo, the swimwear manufacturer that paid him a $1million bonus after Beijing - have stood by their man. But for how much longer, particularly if criminal charges do follow the three-month ban from competition ordered by USA Swimming? The projected $100million fortune that his agents were bragging about after the triumph of Beijing is teetering on a precipice of public opinion.

The pressure has clearly got to America's hero: photographers have been camped outside his home shouting through megaphones to get his attention and he has told his local newspaper that the thought of having his picture plastered all over newspapers around the world for the wrong reason had put the thought of quitting into his mind for the first time.

“What I have gone through in the past week, no one wants to go through. If I decide to walk away, I will decide to walk away on my own terms,” he told The Baltimore Sun.

By last night, Phelps, the 6ft 4in giant, had turned to the only two things that seem to make him feel secure: his mum, Debbie, a school head, and the swimming pool. For someone so physically imposing, who dominated an entire Olympic Games, Phelps comes over as an adolescent in a man's body. In his humiliating apology at the start of the week, his excuse was that he was only 23 and had acted in a “youthful and inappropriate manner”.

But, perhaps his weakness is ingrained. After all, he was convicted of drink-driving only weeks after winning six golds in Athens. He turned to his mum then, too, for solace and it was her gaze that brought him up short this time.

Now there will be plenty of time for thinking in the environment Phelps calls home: the pool. His exposure comes as he steps up training after his break since Beijing. Hours of swimming would be torture for most people but, for Phelps, it will be a chance to escape. “On Monday, we get back to two-a-day practices and I am looking forward to that,” he said. “I feel more comfortable in the pool. This is my home.”

His ban until May means that he should be ready to defend his seven titles at the World Championships in July. He will be physically ready, but Phelps should brace himself psychologically, because his session with a bong will not be easily forgotten by millions of Americans seeing again their fallen hero.

Explore More Sport

• Athletics

• Boxing

• Cycling

• Sailing

• US Sport