* Spanish rider provisionally suspended
* More scientific investigation needed, UCI says
* Contador blames food contamination
Tour de France winner Alberto Contador has been provisionally suspended after testing positive for a "very small concentration" of a banned anabolic agent during the race, cycling's governing body said on Thursday.
The Spaniard, who won his third Tour this year, was tested during the second rest day of the race and the second B test had confirmed the presence of clenbuterol, the International Cycling Union (UCI) said in a statement.
"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," the statement said.
Contador, who is leaving Astana to join Bjarne Riis's Saxo Bank team next season, blamed food contamination for the finding.
"It's possible to put your hand in the fire and not burn yourself. If it had been a clear case of doping it would have come out a week later. The food poisoning came from a cut of meat from Spain," Contador told Spanish radio station Cadena Cope.
"It is Riis Cycling's hope that this case can be resolved in a orderly and timely fashion as it is in the best interests of all parties involved that the proper conclusions are drawn within a reasonable period of time," Saxo Bank said in a statement.
"The team has had and will continue to have the position that cheating of any form will not be tolerated."
Clenbuterol can be abused by athletes to strip fat and enhance muscle size and can have short-term stimulant effects including increasing aerobic capacity, blood pressure and alertness. It has led to bans for cyclists in the past.
The concentration in Contador's A test was "400 time(s) less than what the antidoping laboratories accredited by (World Anti-Doping Agency) WADA must be able to detect," the UCI said in a statement.
"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 B sample that confirmed the first result."
The case would require "further scientific investigation" before any conclusion could be drawn and could take some time, the statement added, providing no further comment.
The finding puts 27-year-old Contador's Tour de France victory with Kazakh-funded Astana in July under a cloud and threatens to leave an indelible stain on the Spaniard, who also won the 2007 and 2009 Tours and is regarded one of the greatest cyclists of the modern era.
Contador's personal press attache Jacinto Vidarte said food contamination was "the origin of the case".
"From the moment he was first informed by the UCI on Aug. 24, Alberto Contador indicated that a contamination of food was the only possible explanation for what happened," his agent said in a statement.
"Since then, he has placed himself in the hands of the cycling authorities with the confidence that this extremely serious problem that has now come to light can be resolved.
"Experts consulted have also signalled that food contamination was the origin of the case, above all taking into account the quantity of (doping) tests Alberto Contador took during the Tour de France.
"(This) enabled the exact moment of the appearance of the substance to be determined as well as the very small amount detected, which rules out any other origin or intent."
The Contador finding is another blow for elite cycling, which has struggled to shake off its image as a sport riddled with drug cheats, and threatens to cast a pall over the road world championships in Australia's port city of Geelong this week.
The Spanish team at the world championships, where the men's time trial world title was being decided on Thursday, declined to comment.
"There is nothing to say about it at this stage," a spokesman said at the team's box in a marquee pitched under overcast skies.