Russian cyclist Alexandr Kolobnev became the first cyclist at this year's Tour de France to fail a doping test, the International Cycling Union said Monday.
The UCI said a urine sample collected from Kolobnev last Wednesday tested positive for a substance called Hydrochlorothiazide, which is a diuretic that can also be used as a masking agent that hides the presence of other drugs. The samples were analyzed at the Chatenay-Malabry laboratory, which is accredited by the World Anti-Doping.
The first positive case at this year's race happened on the Tour's fifth stage -- a flat sprint stage from Carhaix to Cap Frehel.
Tour organizers and French Anti-Doping Agency President Bruno Genevois were not immediately available for comment.
Kolobnev was in 69th place heading into Tuesday's 10th stage.
Kolobnev, who rides for the Katusha team, has four days to request an analysis of his "B" sample.
Katusha sports director Bart Leysen told The Associated Press that Kolobnev was currently meeting with team management and that a decision on whether he continues in the race was likely to be taken later Monday night.
When asked whether Kolobnev would stay in the race, Leysen said "I don't think so."
The UCI can't provisionally ban Kolobnev because Hydrochlorothiazide is classified as a specified substance, which WADA defines as one that is "more susceptible to a credible, non-doping explanation." Its punishment for such a positive test ranges from a warning to a two-year ban.
"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 defense in particular within the legal timeline, which allows four days for him to have his B sample analyzed," the UCI said in its statement.
Positive tests for diuretics are not uncommon in sport.
Brazilian swimmer Cesar Cielo, the 2008 Olympic champion in 50-meter freestyle, and three Brazilian teammates tested positive for the banned substance furosemide in May at a meet in Rio de Janeiro.
Brazil's swimming federation accepted the four swimmers' explanation that they consumed the drug in a contaminated batch of a supplement they regularly used, giving them a warning instead of a ban.
But swimming's governing body appealed Cielo's doping case to the Court of Arbitration for Sport.
Cycling's showcase race has been decimated by doping scandals over the years, with the 2008 race hit by a spate of positive tests for a product called CERA -- a newer form of the banned blood-booster EPO, which enhances endurance.
Tougher new measures seemed to have produced fewer doping cases until defending champion Alberto Contador tested positive for the banned anabolic agent clenbuterol in last year's race.
The three-time Tour champion has been cleared to compete by the Spanish cycling federation, but the UCI and WADA have appealed the ruling to CAS. Should they win the case, which is set to be heard in August, Contador faces the prospect of losing his 2010 title.
The 30-year-old Kolobnev finished 65th in last year's Tour. The former Russian champion had previously ridden in other races for Domina Vacanze, Rabobank, Team CSC and Saxo Bank.