The Court of Arbitration for Sport's anti-doping division has announced it has begun proceedings against medal-winning Russian curler Alexander Krushelnitsky.
Krushelnitsky, who won mixed doubles bronze with his wife Anastasia Bryzgalova, is widely reported to have tested positive for meldonium.
A statement from the anti-doping division (ADD) of CAS read: "The CAS ADD has initiated a procedure involving the athlete Alexander Krushelnitsky (mixed curling; OAR)."
No hearing date has yet been fixed.
Meldonium, which increases blood flow, was found to be used by more than 100 Russian athletes in 2016.
Former world tennis number one Maria Sharapova served a 15-month ban for using the substance after it was added to the World Anti-Doping Agency's prohibited list.
The positive test will ignite further debate about the involvement of Russian athletes at the Games.
The Russian Olympic Committee is under suspension by the IOC following the systemic doping at the Sochi 2014 Olympics.
The International Olympic Committee in December determined that Russian athletes who proved they were clean would be allowed to compete as neutrals in the Games, in a team named the Olympic Athletes of Russia.
The OAR are competing under the Olympic flag and the Olympic anthem is being played at any medal ceremonies they feature in.
There are 168 athletes competing in the OAR team, who have so far won 11 medals, three silvers and eight bronzes - one of them won by Krushelnitsky and Bryzgalova in the first Olympic mixed doubles curling tournament.