Pau - Luxembourg's Frank Schleck, a former podium finisher at the Tour de France, has tested positive for a banned diuretic, the International Cycling Union (UCI) announced on Tuesday.
Schleck, who finished third in 2011, is currently racing the 99th edition with the RadioShack team run by Belgian Johan Bruyneel.
A statement from the UCI said 32-year-old Schleck had been informed of an "Adverse Analytical Finding (presence of the diuretic Xipamide based on the report from the WADA accredited laboratory in Chtenay-Malabry) in the urine sample collected from him at an in competition test at the Tour de France on 14 July 2012."
Schleck "has the right to request and attend the analysis of his B sample".
The UCI, however, indicated it expects Schleck to be immediately suspended, in accordance with strict anti-doping rules at the race.
"The UCI Anti-Doping Rules do not provide for a provisional suspension given the nature of the substance, which is a specified substance.
"However, the UCI is confident that his team will take the necessary steps to enable the Tour de France to continue in serenity and to ensure that their rider has the opportunity to properly prepare his defence in particular within the legal timeline, which allows four days for him to have his B sample analysed."
Diuretics are not performance-enhancing in themselves although they can be used to help riders lose weight, and therefore perform better in the tough mountain stages of the race.
After the second rest day Tuesday, the race resumes Wednesday when the 16th stage takes the peloton over four major climbs towards a downhill finish at Bagneres-De-Luchon.
Schleck, whose younger brother Andy won the race in 2010 after Spain's Alberto Contador was disqualified for doping, sits in 12th place at 9:45 off the pace of race leader Bradley Wiggins of Britain.