Three-time Tour de France winner Alberto Contador tested positive for a banned steroid during this year's race, according to a statement released by his spokesman Wednesday.

Jacinto Vidarte, Contador's publicist, said the substance, identified as clenbuterol, was found in a test taken on July 21. Contador has blamed food contamination as the only possible explanation.

"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," Vidarte said in the release, "making it possible to define precisely both the time the emergence of the substance as the tiny amount detected, ruling out any other source or intentionality."

Contador will hold a news conference on Thursday in Pinto, Spain.

Contador was first made aware of the positive test on Aug. 24, according to statement, and has provided his explanation to the proper authorities.