A Russian medallist at the Pyeongchang Winter Olympics is suspected of having tested positive for a banned substance, a source at the Games said on Sunday, in a potential major blow to Russia’s efforts to emerge from a drug-cheating scandal.

Alexander Krushelnitsky, a bronze-medallist along with his wife in mixed-doubles curling, is suspected of having tested positive for meldonium, the source said. Meldonium increases blood flow which improves exercise capacity in athletes.

Russia has been accused of running a state-sponsored and systematic doping programme for years, an allegation Moscow denies.

Russian sports officials are to meet anti-doping officers at Pyeongchang, the source said, adding that any violation would only be confirmed after analysis of a “B” sample.

An official for the International Olympic Committee (IOC) declined to comment, saying an independent testing authority was in charge of drugs testing at Pyeongchang.

Russian athletes are banned from competing for their country at Pyeongchang due to allegations of systematic doping. They are listed as neutral Olympic athletes, unable to have the Russian anthem played in medal ceremonies or use national symbols.

The IOC has said it may allow the Russians to march with the Russian flag and in national uniform at the Games closing ceremony on February 25th, provided they will have complied with its code of conduct on neutrality.

The code requires compliance with IOC anti-doping rules.