The person spoke on condition of anonymity because he was not authorized to discuss the case.

The Kazakh rider and his Astana team were forced out of the Tour on Tuesday, when it was revealed Vinokourov had failed a doping test. Last Saturday, he tested positive after winning a time trial. On Monday, Vinokourov also won stage 15 _ a tough climb in the Pyrenees.

He faces a two-year ban from cycling and could lose a year's salary under the cycling governing body's anti-doping charter.

Earlier Saturday, Vinokourov announced he would fight any blood doping charges.

"Never before this year's Tour de France have I ever been accused of violating any doping law," Vinokourov said in a statement released by his attorney, Maurice Suh. "I have been tested at least 100 times during my career. These test results simply make no sense. Given all the attention paid to doping offenses, you would have to be crazy to do what I have been accused of, and I am not crazy."

Blood transfusions work by increasing an athlete's count of red blood cells, which carry oxygen to the muscles.

Doping expert Michel Audran, of the University of Montpellier in southern France, said that because blood was used from a compatible donor _ not Vinokourov's own blood _ it's easy to see anomalies when the blood is tested.

Performance can increase between "3 and 20 percent," depending on how much is injected, Audran said. "It helps endurance, working longer and harder."

However, the risk is enormous.