Andre Agassi would have been a pariah in his own sport if his drug-taking exploits had been made public while he was playing, it was claimed last night.

Leading sponsorship experts said that Agassi’s new status as a revered philanthropist would protect him from rejection by the sponsors who now support his charitable causes.

But they were shocked by the revelation that Agassi took crystal methamphetamine, a highly addictive drug, and then lied to the tennis authorities. If that had become public knowledge at the time, they believe he would have been thrown out of tennis so fast there would have been scorch marks on the lawns of Wimbledon.

“There is no question he would have been banned and rejected by every sponsor he had,” Dominic Curran, director at Synergy, the sport sponsorship consultancy, said. “It was not just a question of taking performance-enhancing drugs or a recreational drug but a substance that has horrific consequences.

“Any sponsor would have dropped Agassi like a hot potato and could not countenance being associated with an offence and a lie on that scale.”

Agassi became one of the most sought-after sportsmen in the world, racking up more than £100 million in endorsements during his career — putting him in the same league as figures such as Tiger Woods, Michael Schumacher and Roger Federer.

His journey from scruffy bad boy to clean-cut American idol is the stuff of sporting dreams and was latched on to quickly by sponsors wanting to make the most of a man whose image transcended his sport. Nike, the world’s most powerful sportswear company, started its association with Agassi in 1986, his first year as a professional, handing him $25,000 (about £15,000). But as Agassi moved up the rankings to become an eight-times grand-slam singles tournament winner, the relationship strengthened into a ten-year contract worth $120 million.

Drugs were never on the agenda, though, and perhaps the most telling deal of Agassi’s career was with Canon, the camera manufacturer, as he intoned their slogan in a series of television commercials. The slogan was: “Image is everything.”

Agassi’s detailed confession in his autobiography of how he took the drug and then lied about it is a dent in an image that had seemed so squeaky clean until The Times’ serialisation of his book started yesterday.

“The question is whether a confession like this has an impact on the Agassi brand, built up over years,” Pippa Collett, managing director of Sponsorship Consulting, said. “I think probably not and that people will see this as a confession and that he has come back from a bad place.

“It is always difficult for a sponsor to invest in an individual because you never know when they will fall off the wagon, as it were, such as taking drugs, drinking, driving offences or bad behaviour. Fortunately, Agassi’s career is over so that is not an issue.”

Michael Phelps, the eight-times gold medal-winner at the Beijing Olympics last year, discovered just how fast sponsors can react when Kellogg, the food company, refused to renew its $1 million endorsement deal with him after he was pictured appearing to smoke cannabis through a glass pipe, known as a bong, in January.

Martina Hingis, the former tennis No 1, retired after testing positive for cocaine during Wimbledon in 2007. She was reduced to taking part in this year’s version of the BBC’s Strictly Come Dancing programme, while Phelps is slowly rebuilding his image.

But Agassi, with Steffi Graf, his wife and winner of 22 grand-slam singles titles, have devoted themselves to their charitable foundation, which has raised more than £40 million to educate underprivileged children. His deal with Longines, the Swiss luxury watchmaker, has also been used to raise money for charity.

Deals like that will go on if and when Agassi’s image is rehabilitated, in spite of his drug-taking confessions from a difficult past.