Lance Armstrong has overcome cancer, rival cyclists and nagging allegations of doping to become one of the world’s best-paid athletes and sought-after pitchmen. He’s also turned the Lance Armstrong Foundation, better known as Livestrong, into one of the top 10 groups funding cancer research in the US. Since its inception in 1997, it has raised around $325 million (around Rs1,500 crore), and become synonymous with the 72 million yellow bracelets it has sold bearing the Livestrong name.

The Armstrong brand is one of the best in sports.

Yet, everything the seven-time Tour de France champion has created is now threatened by a new opponent: a US federal investigation. Philanthropy experts say the foundation, in particular, is at risk of losing future donations if its chairman is dragged down in scandal.

Federal prosecutors have been investigating pro cycling since Floyd Landis, a former Armstrong teammate who was stripped of his 2006 Tour title, admitted this year that he used performance-enhancing drugs. Landis also accused many others in the sport, including Armstrong, of doping.

Under scrutiny: Lance Armstrong AP

Last week, prosecutors subpoenaed documents from a 2004 case in which a Texas company with business ties to Armstrong tried to prove he used drugs in order to avoid paying him a performance bonus.

Armstrong has long denied that he used performance-enhancing drugs, and he has not been charged. The foundation has not been accused of wrongdoing, but it is so closely linked with Armstrong that it could be hurt.

“They are not going to be able to thrive if the person who is the spirit behind it is in trouble," says Ken Berger, CEO of Charity Navigator, which analyses around 5,000 non-profits in the US. “It is just going to devastate them."

Although the investigation is ongoing, public opinion may be starting to shift. Words such as “scandal", “lie" and “steroids" are now the most popular phrases used to describe Armstrong, according to Zeta Interactive, a marketing firm that tracks online sentiment. In 2008, when Armstrong was the fourth most talked about athlete, words used to describe him included “hero", “legend" and “Nike"—a reference to one of his main sponsors.

“Anyone or anything associated with Lance Armstrong should be worried right now," Zeta Interactive CEO Al DiGuido says. “He has faced these kinds of allegations before, but the fuel really seems to be kicking in this time."

Fifty-eight per cent of the online sentiment about Armstrong remains positive, according to Zeta’s rating system, but that’s down from 86% at the beginning of July, and it’s the first time it has fallen below 60%.

Armstrong still has legions of fans, including 2.6 million Twitter followers who track his musings on racing and life. His sponsors, for now, are standing behind him. Several of them also support Armstrong’s foundation, which he started after he beat cancer.

As in his cycling career, Armstrong appears to be past his prime as a pitchman. That means the stakes aren’t quite as high for his personal fortune as they were for golfing superstar Tiger Woods, whose marital infidelities cost him lucrative deals with Accenture Llp and AT&T Inc. Woods remained the top-paid athlete on a recently released Forbes list showing him with earnings of $105 million during the year ended June. Armstrong was the 15th highest paid athlete in the same period, with an estimated income of $20 million. That’s down from $28 million in the year ended June 2005, just before he won his seventh straight Tour de France.

Armstrong’s story still resonates with so many people that his foundation sold out of all 130,000 bracelets that it took to France in July, a 30% increase from last year, says foundation CEO Doug Ulman. Those $1 bracelets, meant to be a testament to courage and determination, could become a symbol of shame if it’s proved Armstrong cheated, says DiGuido of Zeta Interactive.

Armstrong says that won’t happen because the allegations are unfounded. “No one on our foundation team is going to be distracted by this witch-hunt," Armstrong said in a statement to The Associated Press. AP