Cyclist Alberto Contador, winner of the 2010 Tour de France, has revealed that he has tested positive for a banned substance.

Contador's press officer said he had tested positive for clenbuterol during a rest on the Tour in July.

In a statement, the spokesman added that the Spanish rider was the victim of "food contamination" and would hold a news conference later on Thursday.

Cycling has struggled with doping allegations for years.

Source : bbc.co.uk