A British cyclist, named as Simon Yates, has failed an in-competition drugs test.
The sport’s governing body, the UCI, notified British Cycling of a “potential anti-doping rule violation” based on an “in-competition sample”.
Proceedings will be managed by the UCI independently, according to a spokesman for British Cycling.
“It would be inappropriate to comment further until the process has been completed,” the spokesman added.
The 23-year-old former points race world champion is regarded as one of Britain’s brightest prospects on the road, along with his twin brother Adam.
Yates, a climber with Australian team Orica-GreenEdg, achieved a top-10 finish on the Mur de Huy stage of last year’s Tour de France, and was seventh in last month’s Paris-Nice race.
The failed test comes in a bad week for British Cycling, with technical director Shane Sutton resigning on Wednesday amid claims of sexism and discrimination.
British Cycling is investigating claims the 58-year-old Australian used derogatory words to describe Para-cyclists, while an independent review will also look into rider Jess Varnish’s accusations that Sutton made sexist comments and told her to “go and have a baby”.
Sutton “rejects the specific claims” but said the allegations against him had “become a distraction” to British athletes before this summer’s Rio Olympics.