The 15-year-old figure skating star Kamila Valieva, who led Russia to team gold at the Beijing Olympics this week, tested positive for a banned heart medication before the Games, Russian media have reported.
The positive test could cost Russia the team gold and also threatens Valieva's participation in the individual event that starts on Tuesday.
Russian athletes are competing in the Beijing Games as the Russian Olympic Committee (ROC) after the country was banned because of a massive state-sponsored doping scheme at the 2014 Sochi Olympics.
The sample in question was obtained before Valieva won the European championship last month, the RBC newspaper reported late Wednesday.
The drug detected is trimetazidine, a metabolic agent that is prescribed for the treatment of angina and vertigo, according to Kommersant newspaper.
It is banned by the World Anti-Doping Agency because it can increase blood flow efficiency and help endurance.
The reports said the test result was the reason that the team medals ceremony was removed from its scheduled slot on Tuesday.
The Russians won the gold medal in the team competition with the United States taking silver and Japan bronze, but the ceremony did not take place as planned.
International Olympic Committee spokesman Mark Adams said on Thursday an "active legal case" was under way concerning the medal ceremony and so he could not comment on the reports.
He said claims that the case concerned doping were "speculation."
"We had a situation arise yesterday that has all sorts of implications," he added.
Asked how long the athletes in the team competition would have to wait to receive their medals, Adams said: "It depends on the legal process and I would imagine everyone is working as quickly as they can.
"We understand for the athletes involved (in the ceremony) that they want to see this come to a good outcome."
In Moscow, Kremlin spokesman Dmitry Peskov dismissed the speculation.
"The scandal broke out not at the Olympics but around the Olympics, and among those who did not have the proper information — as always," he told reporters.
"The only source here can and should be the IOC," he said.
"We wish our athletes, including Valieva, only gold medals."