The Court of Arbitration of Sport (CAS) confirmed on Monday that an anti-doping case has been opened against Russian medal-winning curler Alexander Krushelnitsky.
“Further to a request from the International Olympic Committee (IOC), the CAS ADD has initiated a procedure involving the athlete Aleksandr Krushelnitckii (mixed curling; OAR),” a statement from CAS read.
“No hearing date has been fixed yet and no further information will be provided at this point.”
Krushelnitsky is suspected of testing positive for meldonium.
Reuters originally confirmed the identity of the athlete with a Russian Olympic delegation spokesman, following multiple reports in the Russian media.
A spokesman for the IOC said it would be "extremely disappointing for us if a case is proven".
Meldonium, a substance that increases blood flow and improves exercise capacity, was banned in 2016.
Russian curling federation president Dmitry Svishchev explained to Reuters that the team's curlers had been tested on 22 January, before flying out to South Korea, and that the tests returned then were negative.
"I have known these guys for many years," said Svishchev . "Only a crazy person takes banned substances before a competition, before the Olympics.
"It's a strange story. It raises a lot of questions."
The IOC responded in a statement released on Monday, insisting there was "a strong testing programme" in place at the Games.
It added: "On the one hand it is extremely disappointing when prohibitive substances may have been used, but on the other hand it shows the effectiveness of the anti-doping system at the Games which protects the rights of all clean athletes."The news is be a big blow to Russian attempts to ‘clean up’ their sports and emerge from their doping crisis. It has also embarrassed the IOC. More than 160 competitors are taking part as neutral Olympic Athletes from Russia (OAR) in PyeongChang as Russia was banned from the Games over accusations about running a state-backed, systematic doping programme for years, including at the last Olympic Winter Games, which Russia hosted in Sochi.
Despite Russia being banned from the Games in South Korea, athletes who could prove they are clean could compete under the OAR banner. Team OAR sent 169 competitors to the event and are the third biggest delegation behind Canada and the United States. The Olympic anthem is played at any medal ceremonies they are involved in with no Russian flag or anthem.
The IOC has indicated the Russians may be allowed to march with the Russian flag and in national uniform at the Games’ closing ceremony on February 25, provided they will have complied with its code of conduct on neutrality.