Tour of Turkey winner Mustafa Sayar has been provisionally suspended and faces being stripped of victory after testing positive for the blood-boosting hormone EPO at an earlier race.
The International Cycling Union (UCI) said Sayar had traces of EPO in a urine sample given at the Tour of Algeria on March 11.
The 24-year-old Turkish rider then won his home country's signature event, an eight-day stage race, in April.
The UCI said Sayar had been suspended while the Turkish cycling federation prosecuted a disciplinary case.
Sayar's victory in the Tour of Turkey's sixth stage on April 26 provoked frustration from rivals including German sprinter Marcel Kittel.
"I was not often in my life so angry about a result of someone else. And I see many people around me feeling the same," Kittel, who won two stages, wrote on Twitter.
African road race champion Natnael Berhane of Eritrea is in line for the Tour of Turkey victory if Sayar's doping offence is confirmed.
Berhane, who rides for French team Europcar, won the third stage before finishing runner-up overall.
