Tour de France winner Alberto Contador had eight times the allowable amount of a chemical that indicates doping in his system during this year's race, according to The New York Times.
The newspaper attributes a person with knowledged of the test results on the three-time Tour champion.
A test that the Times said was used for the first time at this year's Tour detected a specific type of chemical, called a plasticizer, that is found in plastic IV bags. Evidence of that chemical in an athlete's urine could mean the athlete has used a blood transfusion to boost endurance.
The World Anti-Doping Agency bans blood transfusions or any intravenous infusions, except in a medical emergency, according to the Times.
The International Cycling Union drug-testing chaperones took the urine sample from Contador on July 20, the eve of the Tour's final rest day, said the person, who wanted to remain anonymous because of an agreement to keep the information confidential while Contador's investigation is continuing, the newspaper reported.
Contador tested positive for clenbuterol one day later, and was subsequently provisionally suspended by the ICU, which could strip him of his Tour crown and suspend him for two years if he is convicted of a doping offense.
Stories out of France and Germany last week also said traces of a plasticizer were found in Contador's urine, the Associated Press reported.
Contador has repeatedly denied doping or having a transfusion, instead blaming the clenbuterol on contaminated meat.