The Spanish superstar cyclist, winner of the prestigious event in July this year, claimed that the banned substance found in his body, clenbuterol, came from food contamination.

Clenbuterol burns muscle and fat and improves breathing. Investigations into the drug have shown that small amounts in the human body can be attributed to food contamination, but significant amounts usually signify deliberate foul play.

In Contador's case, a "very small concentration" of the drug had been found according to the UCI. The cycling body said "further scientific investigation" would be carried out to ascertain whether it was deliberately administered or absorbed through food.

The substance was detected in a urine sample Contador provided during a rest day in this year's tour. A second test, a so-called B-sample, confirmed the presence of the substance.

"The rider … was formally and provisionally suspended as is prescribed by the World Anti-Doping Code," a UCI statement confirmed on Thursday.

Experts support claim that substance may come from food

Contador has apparently consulted with a number of anti-doping experts who have told him that the tiny amount of the substance found in his sample, although large enough to show up in WADA (World Anti Doping Agency) tests, suggests that the cyclist may have fallen victim to food contamination as claimed.

Dutch anti-doping expert Douwe de Boer said the amount points "clearly in the direction of a contamination" and that such a low dose would not help Contador's performance, according to news agency AFP.

Critics point out that after the rest day during which Contador provided the positive urine sample, the Spaniard took two massive steps towards his third title: he equaled the time set by main rival Andy Schleck of Luxembourg in one stage, and then blew Schleck away in the next to secure a 39-second lead with one stage to go.

Clenbuterol hit the headlines in April when Chinese rider Fuyu Li of the RadioShack team, which includes Tour legend Lance Armstrong, was also provisionally suspended after testing positive.

Author: Nick Amies
Editor: Nancy Isenson