PAU, France -- Astana team leader Alexander Vinokourov failed a dope test after winning Saturday's Tour de France time trial, his team announced on Tuesday before quitting the race.
Vinokourov tested positive after showing his time trialling form on the way to victory in Albi on Saturday.
Astana did not give any further details regarding Vinokourov but a cycling source said the Kazakh, who has won two stages on this year's Tour, tested positive for blood doping.
"I cannot comment on this until the result of the B sample's analysis," International Cycling Union (UCI) president Pat McQuaid told Reuters over the phone.
Astana clearly felt they had no option other than to quit the Tour, the 33-year-old Vinokourov having also won Monday's stage in Loudenvielle-Le-Louron.
British rider David Millar, who was holding a press conference in Pau when the news broke, said: " I'm speechless. It makes me sad. I have the impression the riders will never understand."
Millar served a two-year ban and was stripped of his gold medal from the 2003 world championships after admitting taking the banned blood-booster EPO.
Vinokourov looked to have put his injury woes behind him to revive his Tour hopes with an outstanding victory in the individual time trial 13th stage on Saturday.
He decimated his rivals as he clocked one hour six minutes and 34 seconds for the 54 kilometers around Albi, one minute and 14 seconds quicker than second-placed Cadel Evans of Australia.
Vinokourov had ridden himself back into contention after a nasty fall in the first week severely hampered him in the Alpine stages.
"I'm very happy with my performance. I'm very motivated," he said at the time. E-mail to a friend