Frank Schleck, brother of 2010 winner Andy Schleck, has pulled out of this year's Tour de France after failing a drugs test, although he denied any wrongdoing.
The RadioShack-Nissan team member, who finished third in last year's race, tested positive for diuretic Xipamide on July 14. Schleck was 12th in the current standings, 9 minutes and 45 seconds behind leader Bradley Wiggins.
Cycling's world governing body, the Union Cycliste Internationale (UCI), informed Schleck of his drug failure on Tuesday and requested him to withdraw, even though its anti-doping rules do not require an immediate suspension.
In a statement, distributed by the Luxembourg media outlet RTL, Schleck said: "I categorically deny taking any banned substance.
"I have no explanation for the test result and therefore insist that the 'B' sample be tested which is my right. If this analysis confirms the initial result, I will argue that I have been the victim of poisoning."
Team spokesman Philippe Maertens, earlier, said: "He tested positive for Xipamide. It's not a performance-enhancing product, but it's forbidden.
"The team doesn't know where that product comes from. RadioShack will stay in the Tour. He's not suspended. Even the UCI (International Cycling Union) cannot say to him 'you have to go'.
Maertens said Schleck was shocked to receive the news. "It was like he got a hammer on his head. He doesn't know anything about where the product comes from.
"It's a shock for everybody. We're having a good Tour de France.
"We're leading the team classification; it's a big goal for us.
"Without Frank Schleck it's going to be harder. All our riders are working for one goal. When something happens like this you can imagine they are not happy."
An earlier statement from Radioshack read: "Our team attaches great value to transparency. Because of these values, we can announce the following as a response to the adverse analytical finding of Xipamide in Frank Schleck's urine sample of July 14 during the Tour de France.
"After being informed by the UCI about the presence of Xipamide in the urine sample of Frank Schleck on July 14, the team has decided to immediately withdraw Frank Schleck from the Tour de France.
"Even though an abnormal A sample does not require these measures, Mr. Schleck and the team believe this is the right thing to do, to ensure the Tour de France can go on in calm and that Frank Schleck can prepare his defense in accordance with the legal timing to do so.
"On the subject of Xipamide the team can declare the following: it is not a product that is present in any of the medicine that the team uses and 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.
"However, the team is fully determined to collaborate with the anti-doping agencies in order to resolve the matter."
This is the second drug-related incident in this year's Tour de France, after Cofidis suspended Remy di Gregorio, after learning that he may have tried to use banned substances.