Russian curling medallist Alexander Krushelnitsky has been charged with a doping offence at the Winter Olympics in Pyeongchang.
The Court of Arbitration for Sport said it had "initiated a procedure" against the 25-year-old, who won bronze in the mixed doubles with his wife Anastasia Bryzgalova.
He is suspected of testing positive for meldonium, which is designed to boost metabolism and endurance. It is the same drug that saw Maria Sharapova suspended from tennis in 2016 .
No hearing date has been set, but if it is confirmed that he took the drug it could affect Russian athletes' chances of being allowed to march under their own flag at the closing ceremony.
The International Olympic Committee (IOC) suspended the country's federation last year in connection with a doping scheme at the 2014 Games in Sochi, but later said it would allow "clean athletes" to participate under neutral uniforms and without the national flag.
IOC spokesman Mark Adams said Russians have undergone "rigorous testing" to a "significant level more than others".
Krushelnitsky was not with his team on Monday and could be set to lose his medal, with the Norwegian team who finished fourth in line for the bronze if the positive test is confirmed.
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Before the court confirmed it was Krushelnitsky who had been charged, Russian Curling Federation president Dmitry Svishchev said he had tested clean as recently as 22 January - the day before he flew to a pre-Olympic training camp in Japan.
Svishchev said it was possible that his food or drink had been spiked with the drug, and suggested rival athletes or Russia's political enemies could be responsible.
"It can't happen at the Olympic Village because everyone eats the same canteen food," he said.
"It could happen at training camp or in the intervening period.
"There's a possibility of it being something within the team, that something happened during training camp, or as a political means to achieve some goal."
It is the second doping case of the games in South Korea, after Japanese short-track speedskater Kai Saito tested positive for a banned diuretic substance.