PARIS (AP) -- Three-time Tour de France champion Alberto Contador of Spain tested positive for a banned substance in winning this year's race and has been suspended by cycling's governing body.
A World Anti-Doping Agency-accredited lab in Cologne, Germany, found a "very small concentration" of clenbuterol in Contador's urine sample on July 21 at the Tour, according to a statement from the International Cycling Union.
But the amount was "400 time(s) less than what the antidoping laboratories accredited by WADA must be able to detect," the cycling organization said.
Both Contador's A and B samples tested positive and the cyclist has been "formally and provisionally suspended," the UCI said.
If it is proven that Contador cheated, cycling would suffer a devastating blow. Having invested millions of dollars in recent years in what is widely regarded as the one of the most stringent anti-doping regimes anywhere, cycling authorities hoped to be turning the corner on the widespread drug use by riders that had long made a mockery of the sport. Although just 27, Contador is already the greatest rider of his generation and his victories at the Tour and elsewhere were seen as a possible break from cycling's dirty past.
The UCI's statement gave no indication of whether Contador will be stripped of his latest Tour title or be banned.
"The UCI continues working with the scientific support of WADA to analyse all the elements that are relevant to the case. This further investigation may take some more time," its statement said.
Jacinto Vidarte, Contador's publicist, released a statement Wednesday saying the cyclist insists food contamination is the only possible explanation.
"The experts consulted so far have agreed also that this is a food contamination case, especially considering the number of tests passed by Alberto Contador during the Tour de France," Vidarte said in the release, "making it possible to define precisely both the time the emergence of the substance as the tiny amount detected, ruling out any other source or intentionality."
Contador will hold a news conference on Thursday in Pinto, Spain.
Contador was first made aware of the positive test on Aug. 24, according to Vidarte's statement.
In July, Contador won the Tour de France for the third time in four years, beating Andy Schleck of Luxembourg by 39 seconds.
Contador is a lithe but powerful rider who likes to use explosive bursts of speed up sharp mountain climbs to shake off rivals. Having won all three Grand Tours of France, Italy and Spain, something seven-time Tour de France champion Lance Armstrong never achieved in his career, he appeared destined to become one of cycling's all-time greats.
If Tour officials strip Contador of his title, he would be just the second cyclist so punished. The first was American Floyd Landis, who was stripped of his 2006 Tour title after a positive test. For years, Landis denied doping but admitted this spring that he used performance-enhancing drugs. In doing so, he accused Armstrong and others of systematic drug use.
Armstrong and Contador had a fractious relationship when they rode together on the Astana team at the 2009 Tour. Contador won that year, while Armstrong placed third - the first time since 1999 that he had not won. Armstrong said then that Contador has the potential to become a five-time Tour winner.
Clenbuterol is used as a weight-loss drug which builds muscle while burning fat. It is commonly given to horses to treat breathing problems.
American swimmer Jessica Hardy tested positive for clenbuterol at the U.S. trials in July 2008. She served a one-year suspension that ended last summer. The Court of Arbitration for Sport accepted her explanation that she had unknowingly taken the banned anabolic agent in a contaminated food supplement.
A number of athletes have been banned in recent months after using the banned drug, including Polish canoeist Adam Seroczynski, British hurdler Callum Priestley and Chinese Olympic judo champion Tong Wen.
Two cyclists also have been suspended, accused of using the drug. In May, the UCI suspended Italian cyclist 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.
Former New York Mets clubhouse employee Kirk Radomski admitted to distributing clenbuterol to dozens of current and former Major League Baseball players and associates in his plea deal.