Bahrain-Merida rider Kanstantsin Siutsou has been provisionally suspended after testing positive for banned substance EPO.
The UCI, cycling's world governing body, said the 36-year-old was tested out of competition on 31 July.
The Belarusian, who was with Britain-based Team Sky between 2012 and 2015, has the right to request B sample analysis.
Siutsou has also been suspended by Bahrain-Merida, who he joined in 2017.
In a statement, the team said Siutsou was told in June that his contract, which expires on 31 December, would not be renewed.
Bahrain-Merida general manager Brent Copeland said: "This news is terribly disappointing.
"We are very severe with any wrongdoing with regards to our internal health code."
EPO, or erythropoietin, is a blood-boosting hormone that delays the onset of fatigue.