Bradley Wiggins' Tour de France campaign is over after his Cofidis team withdrew because the Briton's team-mate Cristian Moreni failed a drugs test.
Wiggins had performed well in the time trials on the Tour
Moreni, who was Italian champion in 2004, tested positive for testosterone following last Thursday's 11th stage.
Wiggins, the reigning Olympic pursuit champion, was lying 138th - two hours 42 minutes and 20 seconds off the lead.
"I don't want to continue in the Tour de France anyway, it is not supposed to be like this," he told the Guardian.
"It is completely gutting to have to quit the Tour but everyone knows where I stand on doping. I have nothing to hide.
"It's pure stupidity on the part of Moreni. I don't know how he can have slipped through the net.
"It makes you think about your future as a professional cyclist. It makes me question the whole thing, but then you think why not continue because I get a lot of pleasure out of it."
Cofidis team president Francois Migraine said: "It's the only thing to do in such circumstances."
Wiggins finished fourth in the prologue, which was held in London, and fifth in last Saturday's 54km time-trial in Albi.
The 27-year-old would have expected to do well in next Saturday's time-trial between Cognac and Angouleme.
Wiggins' trainer Shane Sutton told Five Live: "Bradley has always been clean from day one and he will be very disappointed.
"One mindless individual has put everybody at risk and it is a shame."
London's mayor Ken Livingstone, who watched Wiggins in the prologue, said: "This is deeply disappointing for Bradley Wiggins, who has had a fantastic Tour de France.
"As a steadfastly clean rider, he is well-known for his vocal condemnation of drug use in his sport, and has been a tremendous ambassador for London and cycling."
Cofidis are one of 11 teams not to win a stage yet.
Their voluntary withdrawal leaves 19 teams in the race after Astana were asked to withdraw following Alexandre Vinokourov's positive test.
Vinokourov, a pre-race favourite, tested positive for blood doping after winning last Saturday's time-trial stage.
The Kazakh rider reportedly had two different kinds of red blood cells, indicating he has taken blood from someone of a compatible group.
Just 24 hours later, Moreni became the second competitor to fail a drugs test.
The Italian was questioned by police and Cofidis team manager Eric Boyer told Reuters: "He accepted his wrongdoing and did not ask for a B-sample."