Olympic medallist Anna Chicherova has vowed to clear her name after learning she is one of 14 Russian athletes to have failed a doping retest.
The high jumper won bronze in 2008 but that result is now in doubt after 454 samples from those Games were retested.
"It's the most complete shock," said Chicherova, who went on to win gold at the 2012 Games in London.
"I can't explain how it could have happened. I was always sure what supplements and medicines I was using."
Earlier this month, the International Olympic Committee said up to 31 athletes from around the world could be banned from the Rio Olympics as a result of the retests, which were conducted using the latest scientific methods.
The Russian Olympic Committee subsequently revealed that 14 of those 31 athletes were Russian.
A Russian TV report then claimed those 14 athletes included 10 medallists, among them 33-year-old Chicherova, who is planning to defend her Olympic title at the Rio Games, which begin on 5 August.
Sports minister Vitaly Mutko admitted the news did not "look good" but said the results were "not an objective picture" of Russia's doping situation.
Russia's athletes are already banned from international competition following allegations of state-organised doping.
But in an interview with BBC sports editor Dan Roan, Mutko said he expected the ban to be lifted for Rio because it would be "useless" for the International Association of Athletics Federations (IAAF) to continue punishing them.
He also held the IAAF partly responsible for Russia's predicament, claiming it helped cover up the positive tests.
"The priority for them [IAAF] must be the development of track and field worldwide and you cannot achieve that with punishment," he said.
"It damages hugely the reputation and image of track and field. It would decrease the popularity of the sport in Russia. Kids would not want to do it."