The results and reputation of three-time Tour de France winner Alberto Contador of Spain hang in the balance after his spokesman announced Wednesday that Contador tested positive for a trace amount of clenbuterol, a banned substance most commonly prescribed as an asthma medication.

Contador, who has not raced since clinching his third Tour victory in Paris on July 25, has been suspended since late August, when he was informed his A sample had tested positive. He has not yet been declared guilty of an official doping violation, according to international cycling authorities.

Alberto Contador won his third Tour de France title in July. Bryn Lennon/Getty Images

At a news conference Thursday in his hometown of Pinto, Spain, outside Madrid, Contador blamed contaminated meat for the positive doping test and called the UCI's suspension "a true mistake."

Contador called it "a clear case of food contamination."

Contador 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 the team was staying.

Contador said he ate the meat on July 20 and again on July 21.

"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," Jacinto Vidarte, Contador's publicist, said earlier in a release e-mailed to reporters.

There have been several anecdotal reports of people becoming ill from meat contaminated by clenbuterol in recent years, as the drug is sometimes used to reduce fat in livestock. However, the World Anti-Doping Agency's strict liability standard allows athletes little if any wriggle room when they test positive for a banned substance.

The urine sample in question was taken from Contador on July 21, the second rest day of the 2010 Tour. Contador all but clinched the Tour title July 22 in the Pyrenees, when he battled Luxembourg's Andy Schleck to a stalemate on the uphill finish of the Col du Tourmalet. Contador maintained his narrow lead in the Tour's final time trial, ultimately prevailing by a 39-second margin. He was first made aware of the positive test Aug. 24, according to Vidarte's statement.

Clenbuterol is a synthetic bronchodilator often prescribed to asthma sufferers. The drug is on the WADA's banned substances list, and if Contador's positive test result is upheld, he could face a mandatory two-year ban from the sport.

Why the positive test result took more than two months to emerge is unknown. By contrast, Floyd Landis' positive test for synthetic testosterone -- a result that eventually led to his conviction and the stripping of his Tour victory -- became public about a week after his sample was taken.

The UCI statement said Contador's sample was analyzed by the WADA-accredited laboratory in Cologne, Germany.

"The concentration found by the laboratory was estimated at 50 picograms (or 0,000 000 000 05 grams per ml) which is 400 times less than what the anti-doping laboratories accredited by WADA must be able to detect," the UCI statement said.

"In view of this very small concentration and in consultation with WADA, the UCI immediately had the proper results management proceedings conducted including the analysis of [the] B sample that confirmed the first result. The rider, who had already put an end to his cycling season before the result was known, was nevertheless formally and provisionally suspended as is prescribed by the World Anti-Doping Code.

"This case required further scientific investigation before any conclusion could be drawn. The UCI continues working with the scientific support of WADA to analyze all the elements that are relevant to the case. This further investigation may take some more time."

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."

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 were also found in his urine in the two days after the positive result but were so minute that the UCI classed them as negative.

All of Contador's tests before July 21 were negative, De Boer said. The July 21 test was conducted on a rest day at the Tour, when the race was near France's border with Spain. De Boer said friends from Spain visited Contador and brought meat with them -- he believes it was beef -- "to celebrate their meeting."

"My conclusion is that it is very likely that this extra-low concentration [of clenbuterol] entered his body without him knowing it and one of the scenarios is contaminated meat," de Boer said in a telephone interview. He said the UCI's "lack of speed" in deciding whether to sanction Contador suggests that the cycling body is "seriously" considering the argument that contaminated food was to blame.

Clenbuterol has figured into at least two recent doping cases.

American swimmer Jessica Hardy voluntarily withdrew from the 2008 Olympic team after testing positive for the substance. An arbitration panel later agreed with her contention that she had ingested the substance inadvertently, perhaps in a tainted nutritional supplement, and cut her suspension from two years to one.

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 International Cycling Union 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 a plea deal.

Fellow cyclist David Millar, competing at the road cycling world championships in Australia, said Contador deserves the benefit of the doubt until all the facts are known.

"At the moment it doesn't make much sense in that it was a rest day control and it's a micro-dose ... Alberto gets controlled every day when he's in the yellow jersey and that would have come up the day before or after the race," Millar said. "I 100 percent give Alberto fully the benefit of the doubt."

Contador, 27, has been considered the most talented rider in the world over the past four years, winning all five of the Grand Tours, or three-week stage races, he has entered since 2007.

He was a protégé of veteran Spanish team director Manolo Saiz, who was discredited for his links to the 2006 Operacion Puerto blood doping scandal. Contador was part of the Astana-Wurth team that was prevented from starting that year's Tour de France because several team members were implicated in that scandal, which centered on a Madrid clinic. He was initially linked to the affair but later cleared by Spanish authorities.

The following year, Contador, riding for the U.S.-based Discovery Channel team, won a chaotic Tour after Danish rider Michael Rasmussen -- who had all but sealed overall victory by besting Contador in the mountains -- was fired by his own team for lying about evading anti-doping tests and was forced to abandon the race.

When Discovery folded, Contador migrated with manager Johan Bruyneel, who directed all seven of Lance Armstrong's Tour victories, to the Kazakhstan-sponsored Astana team in 2008. That team was not invited to the Tour de France that year by organizers who cited doping violations under previous management. Contador maintained his stature at the top of the sport by winning the Tour of Italy and the Tour of Spain that season.

Armstrong's 2009 comeback after three years away from the sport created a tense environment at Astana as he and Contador vied for team leadership. The two sparred openly for months, but Contador prevailed on the road, winning his second Tour de France that year. Armstrong subsequently departed for the new RadioShack team, and Contador won his third Tour this summer with a team built solely to support him -- although he was not nearly as dominant as he had been in his previous two championships.

After this year's Tour, Contador announced that he had signed with the Danish Saxo Bank team owned by Bjarne Riis. Riis, the 1996 Tour winner who confessed to doping more than a decade later, is one of the most successful businessmen and tacticians in the sport. However, Saxo Bank began to fragment this summer when most of its stars, including brothers Frank and Andy Schleck of Luxembourg, announced they were defecting to join a new Luxembourg-based team.

Andy Schleck finished second in the Tour and would be declared the winner if Contador was disqualified for a doping offense. That turn of events would also throw Riis' 2011 plans into disarray.

Bonnie D. Ford covers tennis and Olympic sports for ESPN.com. The Associated Press contributed to this report.