Italian Luca Paolini has been provisionally suspended after the Katusha rider failed a dope test for cocaine on the Tour de France.
"In accordance with UCI anti-doping Rules, the rider has been provisionally suspended until the adjudication of the affair," the sports governing body said in a statement.
The UCI said that the sample was collected on Tuesday.
Paolini, 38, won the Ghent-Wevelgem classic this year. He also won one stage on the Giro d'Italia in 2013 and another one on the Vuelta in 2006.
On the Tour de France, he was one of the lieutenants of top sprinter Alexander Kristoff of Norway.
Cocaine is a stimulant that is banned in competition.
Paolini is the first rider to fail a dope test on the Tour since 2012, with no rider testing positive on the world's biggest race in the two editions since then.
The last rider to fail a dope test on the Tour de France was Luxembourg's Franck Schleck who was withdrawn from the race after testing positive for a banned diuretic.
He was eventually banned for one year.