If professional cycling was a Hollywood starlet, it would have just emerged from rehab, teetering on the edge of another relapse. The sport’s reputation has long been tainted by those who have resorted to doping and a handful of such offenders are found every year.

In the 2007 Tour de France dual stage winner Alexandra Vinokourov was found guilty of doping and his Astana team immediately withdrew from the race. The following year, teammates Riccardo Ricco and Leonard Piepoli were fired from the Saunier Duval squad after both riders admitted to taking the banned substance, MIRCERA. In the 2009 Tour de France, stage 16 winner Mikel Astarloza was found guilty of doping in the weeks leading up to the race.

While this year’s Tour de France yielded no cases of doping, there is a storm brewing and it hangs directly over the sport’s greatest champion, Lance Armstrong.

According to Armstrong’s former teammate Floyd Landis – the man who was stripped of his 2006 Tour de France victory after failing a drug test – Armstrong used banned substances in 2002 and 2003 while riding for the U.S Postal Service team. While Armstrong has denied the claims, the World Anti-Doping Agency (WADA), International Cycling Union (UCI) and US Anti-Doping Agency (USADA) have all signalled their intentions to investigate Landis’ allegations.

But Landis isn’t alone in making allegations against Armstrong. Three-time Tour de France winner Greg LeMond told The Denver Post that the upcoming doping investigation would find “overwhelming” evidence of wrongdoing on Armstrong’s behalf.

In fact, Armstrong’s career has been littered with allegations of doping. On one such occasion, the French newspaper L’Equipe claimed that six of Armstrong’s urine samples from the 1999 Tour de France had been found to contain the banned substance EPO. At the time, drug tests weren’t able to detect EPO – a hormone which induces red blood cell production – but later tests apparently found evidence of EPO use.  In 2008 Armstrong refused further testing on the samples on the grounds that they had not been properly maintained.

Despite this and other accusations levelled at Armstrong throughout his career, the seven-time Tour de France winner has never tested positive to an official drug test. The agencies responsible for investigating Landis’ claims will be hoping they don’t find cause to disrupt that record.

While the suspensions faced by riders like Vinokourov and Landis have damaged the reputation of professional cycling, to find Armstrong guilty of doping would be catastrophic for the credibility of the sport. After all, with the greatest story in cycling history, Armstrong has the most to lose.

After being given a minimal chance of surviving a bout of cancer that affected his lungs, testicles and brain, Armstrong not only made a comeback to professional cycling but managed to win the sport’s greatest race, the Tour de France, seven times in a row. The Texan’s cancer-comeback and unprecedented success at le Tour resulted in a huge increase in the sport’s popularity in the US and around the world. During Armstrong’s reign, television audiences for the Tour de France increased significantly and USA Cycling memberships rose considerably.

But for all of Armstrong’s influence on the popularity of the sport, the hard work will all be undone if he is found to have doped his way to the top. His frequent claims of innocence, his apparent “six hours a day” on the bike in lieu of drugs and his good-guy persona will all count for nothing if Landis’ damaging claims are proven to be true.

For the sake of the sport we can only hope that Floyd Landis is being as dishonest now as he was in 2006.