PINTO, Spain -- Alberto Contador blamed it all on a bad piece of filet mignon, and promised he would prevail in the end.
The three-time Tour de France winner said contaminated meat caused his positive doping test for a "very small concentration" of the banned substance clenbuterol. It was found in his urine sample on July 21 at the Tour, according to the International Cycling Union, the sport's governing body.
"The idea of anyone questioning my Tour victory does not worry me," the Spanish cyclist said. "I am not going to let something like this destroy everything I have done."
He was provisionally suspended after a World Anti-Doping Agency lab in Germany determined both A and B samples were positive.
The UCI said the amount of clenbuterol in Contador's sample was "400 time(s) less than what the antidoping laboratories accredited by WADA must be able to detect."
Speaking at a news conference in his hometown near Madrid, Contador said, "I think this is going to be resolved in a clear way. With the truth behind you, you can speak loud and clear, and I am confident justice will prevail."
Contador said the beef was brought across the border from Spain to France by a Spanish cycling organizer, Jose Luis Lopez Cerron, during a Tour rest day and at the request of the team's chef. Cerron said earlier Thursday on Spanish radio that he was a friend of the chef, who had complained of poor quality meat at the hotel where the team was staying.
Lopez Cerron said he bought filet mignon for the team in the Spanish border town of Irun on his way to Pau, France.
Clenbuterol is sometimes given to cows, pigs and other animals to increase their growth rate.
Contador said he and four other Astana teammates ate the beef on July 20 and that he was the only one who underwent a doping test on July 21. He ate more of the meat that day, explaining that although it wasn't normal to eat steak a day before racing, it was too good to waste.
He said he learned of the test results on Aug. 24 and met with UCI doctors two days later.
"On the 26th we talked at length about how all this had happened. The UCI itself told me to my face that it was a case of food contamination," Contador said.
The Spaniard said he decided to go public because a German television station was aware of the case, but said it would have been better for cycling's image if it could have been handled internally. He called his suspension by the UCI "a true mistake."
Contador beat Andy Schleck of Luxembourg by 39 seconds in winning his third Tour in four years.
"What a crazy day in cycling with the news about Contador," Schleck said on Twitter. "I only heard about it in the press. I hope he is innocent and I think he deserves the right to defend himself now."
The allegations are the latest to hit a sport whose credibility has been battered by doping scandals. Within hours of Contador's case becoming public, the UCI announced that two Spanish riders failed drug tests during the Spanish Vuelta in September -- runner-up Ezequiel Mosquera and David Garcia. The UCI said they tested positive for hydroxyethyl starch, which increases blood volume.
With seven-time Tour champion Lance Armstrong now back in retirement, Contador is cycling's biggest star, so it could be devastating for the sport if the Spanish rider is found to have cheated.
The UCI's statement gave no indication of whether Contador will be stripped of his latest Tour title or be banned.
If Tour officials do reclaim his title, Contador would be just the second cyclist to be forced to relinquish it. 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.
By investing millions of dollars in recent years in what is widely regarded as one of the most stringent anti-doping regimes anywhere, cycling authorities hoped to eradicate widespread doping by riders, particularly in their showcase race. Although just 27, Contador is already the greatest rider of his generation. His victories at the Tour starting in 2007 and at other major races were seen as a possible break from cycling's dirty past.
WADA director general David Howman told The Associated Press that testing positive for even the most minute amounts of clenbuterol could be enough to sanction an athlete, although he declined to discuss the specifics of Contador's case.
"The issue is the lab has detected this. They have the responsibility for pursuing. There is no such thing as a limit where you don't have to prosecute cases. This is not a substance that has a threshold," said Howman, reached by telephone as he was changing planes in Dubai on his way to the Commonwealth Games in India.
"Once the lab records an adverse finding, it's an adverse finding and it has to be followed up."
"Clenbuterol is a substance that has been used for over 20 to 30 years," he added. "It is not anything new. Nobody has ever suggested it is something you can take inadvertently."
Douwe de Boer, a Dutch anti-doping expert hired by Contador to study his test, said the rider told him that smaller traces of clenbuterol also were found in his urine in the two days after the positive result but were so minute that the UCI classed them as negative.
Clenbuterol has anabolic properties that build muscle while burning fat. It is commonly given to horses to treat breathing problems. In medicine, it is used to treat asthma. In similar ways to stimulant drugs such as amphetamine or ephedrine, it can increase the heart rate and body temperature