Tour de France champion Floyd Landis tested positive for high levels of testosterone during the race, his Phonak team said on Thursday.
The statement came a day after the UCI, cycling's governing body, said an unidentified rider had failed a drug test during the Tour.
The Swiss-based Phonak said in a statement on it Web site that it was notified by the UCI on Wednesday that Landis' sample showed "an unusual level of testosterone/epitestosterone" when he was tested after stage 17 of the race last Thursday.
"The team management and the rider were both totally surprised of this physiological result," the statement said. Phonak said Landis would ask for analysis of his backup "B" sample "to prove either that this result is coming from a natural process or that this is resulting from a mistake."
Landis has been suspended pending the results. If the second sample confirms the initial finding, he will be fired from the team, Phonak said.
Landis won the Tour de France on Sunday, keeping the title in US hands for the eighth straight year. Lance Armstrong, long dogged by doping whispers and reports that he has vehemently denied, won the previous seven.
Speculation that Landis may have tested positive had spread earlier Thursday after he failed to show up for a one-day race in Denmark on Thursday. A day earlier, he missed a scheduled event in the Netherlands.
On the eve of the Tour's start, nine riders, including pre-race favorites Jan Ullrich and Ivan Basso, were ousted, implicated in a Spanish doping investigation.
The names of Ullrich and Basso turned up on a list of 56 cyclists who allegedly had contact with Spanish doctor Eufemiano Fuentes, who's at the center of the Spanish doping probe.