Frank Schleck of Luxembourg pulled out of the Tour de France on Tuesday after failing a doping test.
Cycling's governing body said Schleck tested positive for a banned diuretic, reviving the doping cloud over cycling's biggest event.
The 32-year-old RadioShack Nissan Trek leader placed third in the Tour last year, and was in 12th place overall — 9 minutes, 45 seconds behind leader Bradley Wiggins — on Tuesday's rest day.
Governing body UCI said the diuretic Xipamide turned up in an anti-doping test conducted by the French anti-doping lab in Chatenay-Malabry south of Paris on a sample from Schleck taken July 14.
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.
RadioShack team spokesman Philippe Maertens told The Associated Press in a text message that Schleck had left the Tour, but did not comment further.
The UCI said in a statement it believed RadioShack would "take the necessary steps to enable the Tour de France to continue in serenity" and give Schleck the change to prepare his defence.
The UCI said Schleck has the right to request a test of his B sample. It said the "legal timeline" allows four days for Schleck to have the backup sample analyzed.