Italian Luca Paolini has been provisionally suspended after the Katusha rider failed a dope test for cocaine on the Tour de France, his team and the International Cycling Union (UCI) have said.
"In accordance with UCI anti-doping Rules, the rider has been provisionally suspended until the adjudication of the affair," the UCI said in a statement.
The sport's governing body said that the sample was collected on Tuesday.
"He is going back home," a team spokesman told Reuters.
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