The RadioShack Nissan Trek team pulled Frank Schleck, one of the biggest names in pro cycling, out the Tour de France on Tuesday after he failed a doping test, threatening to overshadow Bradley Wiggins' bid to win the three-week race in Paris this weekend.

The 32-year-old rider from Luxembourg, who was third in last year's Tour, left a police station in Pau where he had discussed the case with authorities after cycling's governing body announced the positive test.

The International Cycling Union, or UCI, said Schleck had tested positive for banned diuretic Xipamide in an anti-doping test conducted by a French anti-doping lab on a sample taken from him on July 14.

It marked the second doping scandal to hit this Tour, and was another reminder of the doping cloud that has damaged the image of cycling and its biggest event for years.

Schleck, the RadioShack leader, had been in 12th place overall - 9 minutes, 45 seconds behind leader Wiggins - going into the second and latter rest day on Tuesday.

The revelation was likely to add stress on the crash-and sickness-depleted pack, just as they were gearing up for two grueling days in the Pyrenees starting Wednesday.

Wiggins, who is aiming to become Britain's first Tour champion, leads fellow Briton and Sky teammate Christopher Froome by 2:05 and Vincenzo Nibali of Italy by 2:23. Defending champion Cadel Evans of Australia is fourth, 3:19 behind.

Competitors in the 99th Tour had plenty of time to ponder the tricky 16th and 17th stages on the rest day, with the Pyrenees visible on the horizon from the medieval, palm tree-lined city of Pau.

Wednesday's stage runs through the so-called "Circle of Death" along four brutal climbs - none more daunting than the 7,000-foot Tourmalet. On Thursday, the last summit finishes atop the 5,300-foot Peyragudes.

Wiggins is talking a big game in his bid to become Britain's first Tour de France champion. He says Wednesday's stage "isn't any more difficult than any other stage we've done up to this stage, really."

Wiggins said the Tourmalet was nothing special.

"It goes uphill like all the others, doesn't it?" he said.

The four renowned passes the riders will climb Wednesday are the Peyresourde, Aubisque, Aspin and Tourmalet, the highest point on this year's Tour. The pack on Thursday must ascend the Col de Mente and Port de Bales before scaling Peyragudes.

"Generally, the Pyrenees are a bit harder than the Alps," said U.S. cyclist Tejay van Garderen. "The roads are a bit rougher. They're just a bit more taxing."

But the more immediate question for the whole pack was how it would surmount cycling's latest positive test for doping - this time at the heart of a well-known cycling family and one of its big-name teams.

The RadioShack team said in a statement that it had decided to withdraw Schleck from the race, and said that the diuretic is not present in any medicine used by the team.

The statement said "the reason for the presence of Xipamide in the urine sample of Mr. Schleck is unclear to the team. Therefore, the team is not able to explain the adverse findings at this point."

Team spokesman Philippe Maertens said Schleck went to the Pau police station of his own accord to cooperate with authorities. Maertens said the rider knew police would likely be coming for him.

Maertens said the team is likely to ask for the "B" sample to be analyzed. That request must come within the next four days, according to the UCI.

"If it comes back positive he will be suspended by the team," Maertens said.

He added that police did not search the riders' rooms at the hotel, and that RadioShack will continue to compete in the race, he said.

Still, it was more bad news for the RadioShack squad, which was built on the remains of former teams of Lance Armstrong, who helped land the top-line sponsorship of the American retail chain for the team.

The team manager, Johan Bruyneel, has been targeted in the same U.S. anti-doping case targeting the seven-time Tour champion. Bruyneel opted to skip the Tour to avoid being a distraction to the race and RadioShack riders.

Schleck's younger brother and RadioShack teammate, Andy, was awarded the 2010 Tour victory after Alberto Contador was stripped of the title over his positive test for clenbuterol.

The younger Schleck is missing this year's race because of a spinal injury.

The case is also likely to cast new doubt on cycling's ability to root out drug cheats despite vigorous controls put in place by the UCI and its allies in the anti-doping fight.

It is the second doping-related case to emerge at the Tour this year. Cofidis rider Remy Di Gregorio of France was arrested on the first rest day on July 10 as part of a Marseille doping probe.

The diuretic is classified as a specified substance and does not require a provisional suspension. The World Anti-Doping Agency defines specified substances as those that are "more susceptible to a credible, non-doping explanation." Bans for such substances are often shorter, and athletes have a better chance of proving that they did not intend to consume it or enhance their performance.

Contacted by phone by The Associated Press in Mondorf-les-Bains, Luxembourg, Frank's 36-year-old brother Steve said he had tried to contact the RadioShack rider by phone but was not successful.

"We're a little bit shaken up," Steve Schleck said.