A Russian athlete at the Pyeongchang Winter Olympics has been implicated in a doping case involving the banned substance meldonium, a source close to the situation told AFP on Sunday.
It comes after a spokesman for the Olympic Athletes from Russia said one of its competitors committed a "possible violation of anti-doping rules", according to Russian media.
If the case is confirmed, it will come before the Court of Arbitration for Sport, which is handling doping matters at the Olympics and has an ad hoc division in Pyeongchang.
Russia are banned from the Olympics over systemic doping, but 168 Russian athletes deemed clean are competing in Pyeongchang under the neutral banner of Olympic Athletes from Russia.
A fresh doping case would be deeply embarrassing and could affect deliberations on whether to lift Russia's ban in time for the Pyeongchang closing ceremony.
"Today the headquarters of our delegation received an official notice from the IOC regarding a possible violation of anti-doping rules," Konstantin Vybornov, spokesman for the Russian team, was quoted as saying by Russian media.
"We are not naming the athlete or the discipline until the B-sample results, which are expected within approximately 24 hours."
The International Olympic Committee suspended Russia in December after revelations of a widespread and highly orchestrated doping conspiracy, which first emerged before the Rio 2016 Summer Games.
Investigations found that the doping plot, straddling several years, culminated when Russia hosted the Sochi 2014 Winter Olympics, where they topped the medals table.
Russian athletes in Pyeongchang are under strict instructions to honour the "letter and spirit" of guidelines governing their participation, including not waving the Russian flag or wearing its colours.
An IOC implementation panel is due to consider how well the Russian team has observed the guidelines before making a recommendation on whether to lift the ban.
Meldonium was added to the World Anti-Doping Agency's list of banned substances in 2016. Russian tennis player Maria Sharapova, a former world number one, served a 15-month ban after testing positive for meldonium early that year.
Russian short track speed skater Semen Elistratov, who won bronze in the men's 1,500m in Pyeongchang, served a brief ban for the same substance in 2016.
Richard Budgett, medical director for the International Olympic Committee, said it seemed that Elistratov took the drug before it was banned.
"Because of the way it's metabolised, it can stay in the system for many, many months, even nine months after it had been taken," Budgett told journalists last week.
He added: "We have to be realistic -- meldonium was used in a widespread way throughout Eastern Europe and Russia and was considered to be a tonic, a type of cardiac stimulant that was not prohibited.
"But of course, quite rightly it was then prohibited and because it was such widespread use there were a large number of cases."