Semen Elistratov, who took bronze in the men's 1,500m short track speed skating ysterday, was briefly suspended in 2016 after testing positive for meldonium -- the same substance that saw Maria Sharapova banned.
The 27-year-old Elistratov is one of 168 athletes competing as a neutral "Olympic Athlete from Russia", after Russia's team was suspended as punishment for systemic doping.
Richard Budgett, medical director for the International Olympic Committee, said meldonium was a "special issue" and it seemed that Elistratov took the drug before it was banned at the start of 2016.
"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 said.
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"So if the cases were consistent with meldonium intake before it was prohibited, then that would not be considered an anti-doping rule violation.
"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.
- 'High-risk group' -
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Elistratov reportedly also took aim at the "hard and unfair" exclusion of many Russian athletes, comments that will be scrutinised as the IOC considers lifting Russia's Olympic ban in time for the February 25 closing ceremony.
Budgett said the Olympic Athletes from Russia had been heavily tested before the Games and remained under scrutiny in Pyeongchang, where about 2,500 doping controls were expected.
"The Olympic Athletes from Russia obviously were a major focus for both the pre-Games taskforce and now at the Games," he said.
"Clearly there's a history of doping in Russian athletes so they're in a high-risk group," Budgett said. "In the pre- Games testing... they've been tested far more than any other athletes."
The last Winter Olympics at Sochi in 2014 was marked by flagrant cheating by Russia, who used a "mousehole" in the laboratory wall to switch dirty samples.
Budgett promised there would be no repeat in Pyeongchang, where the laboratory is under round-the-clock video surveillance and will be monitored by experts from the World Anti-Doping Agency and the IOC.