Three-time Tour de France champion Alberto Contador has claimed he is the victim of contaminated food after testing positive for a banned drug.
The muscle-building and fat-burning drug clenbuterol was detected in his system during this year's Tour.
Contador, 27, the greatest rider of his generation, said that contaminated meat brought in from Spain was responsible for his positive test on 21 July.
"It is a clear case of food contamination," stated the Spaniard.
Contador, who called himself a "victim", has been provisionally suspended by cycling's world governing body the UCI after his A and B samples tested positive.
A World Anti-Doping Agency-accredited lab in Cologne, Germany, found a "very small concentration" of clenbuterol in Contador's urine sample on 21 July at the Tour, according to the UCI.
Spain's Alberto Contador is cycling's biggest star
However, the amount was 400 times less than the 50 picogram benchmark measurement that anti-doping laboratories accredited by Wada must be able to detect.
BBC Radio 5 live's cycling reporter Simon Brotherton said that if the test failure is upheld, Contador could be stripped of his Tour de France title and also given a two-year ban from the sport as a first offender.
"But it sounds to me as if the UCI feels it's such a miniscule amount, and not one that would have potentially made any difference [to his performance], that it is keen to get to the bottom of this and feels it is worth investigating the claims Contador has made," he added.
The only previous Tour winner to be stripped of their title was Floyd Landis in 2006.
The American's allegations about drug use in the sport are part of an ongoing investigation by federal authorities in the United States.
Contador, who in August joined Bjarne Riis's Team Saxo Bank on a two-year deal after leaving the Astana team, said the meat was brought across the border from Spain to France during a rest day during the Tour.
He said there were complaints about the food at the hotel where his Astana team were staying.
The Spaniard revealed he ate the meat on 20 July and again on 21 July and at a specially arranged news conference in his home town of Pinto, he called the UCI's suspension of him "a true mistake".
He claimed: "The UCI itself affirmed in front of me that it was a case of food contamination.
"This is a genuine mistake. I think it will be resolved in a clear way, with the truth up front," he said but added that the UCI "understands that is a special case, which has to be examined".
The rider, who appeared tense and sometimes on the verge of tears, stated he was "sad and disappointed but with my head held high".
He added: "I've spent a month and half keeping this inside, without sleeping. My family didn't find out until last night.
"This is a real error. The system is very questionable and it has to be changed. I cannot tolerate the idea of a possible sanction."
Contador's suspension is a huge blow to the sport, which has fought hard in the past few years to fight widespread doping by riders that has repeatedly sullied the Tour, its showpiece race.
Despite his protestations, the failed test threatens to leave an indelible stain on the record of the Spaniard, who also won the 2007 and 2009 Tours.
It makes no sense because it would have come up in other [doping] controls
But British world time trial silver medallist David Millar backed Contador as a "fantastic athlete and a great human being" and believes the case should never have been made public because further investigation is needed.
Millar, who was banned from cycling for two years in 2004 after admitting to using the blood-booster EPO earlier in his career, feels there are a lot of questions that need to be answered before judging Contador.
"I think there's a very strong chance that this is being blown way out of proportion... because it's a micro-dose and it was on a rest day," said the Scot.
"It makes no sense because it would have come up in other [doping] controls. It's a shame that it has been released when it hasn't been resolved. It's something that should be resolved behind closed doors.
"There are strict rules and I think unfortunately in cycling, for the right reasons, we always jump to the worst-case scenario and because of the history we have in the sport unfortunately maybe Alberto's been thrown to the sharks.
"I think it will get resolved, and I hope so for Alberto's benefit and I hope so for the sport's benefit."
Clenbuterol can strip fat and enhance muscle size and can also have a short-term stimulant effects, including increasing aerobic capacity, blood pressure and alertness. It has led to bans for cyclists in the past.
In similar ways to stimulant drugs such as amphetamine or ephedrine, it can increase the heart rate and body temperature.
Contador earned his third Tour de France victory this year
Athletes and body builders are thought to use it in combination with other performance-enhancers such as growth hormone and steroids to build and define muscles.
It is listed by Wada as an anabolic agent that is prohibited for use by athletes at all times, both in and out of competition.
American swimmer Jessica Hardy tested positive for clenbuterol at the US trials in July 2008 and served a one-year suspension that ended last summer.
But the Court of Arbitration for Sport later accepted her explanation that she had unknowingly taken it in a contaminated food supplement.
A number of athletes have been suspended in recent months after using the banned drug, including Polish canoeist Adam Seroczynski, British hurdler Callum Priestley and Chinese Olympic judo champion Tong Wen.
In May, the UCI suspended Italy's Alessandro Colo after he tested positive for clenbuterol during the Tour of Mexico in April.
And Chinese rider, Li Fuyu, a member of Lance Armstrong's Team RadioShack, was suspended in April after testing positive for the drug during a Belgian race.
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