Russian news agencies are reporting that swimming champion Yulia Yefimova could be facing a lifetime ban from the sport after she tested positive for meldonium.
The four-time breaststroke world champion, who has been based in the United States since 2011, tested positive for the drug during an out of competition test, media reported on March 16.
Yefimova, 23, a bronze medallist at the 2012 London Olympics who was considered Russia's best hope for winning a medal at the upcoming Olympics in Rio, could be handed a lifelong ban because she has previously failed a drug test.
In May 2014, she was disqualified for 16 months by the International Swimming Federation after a test found traces of the anabolic steroid DHEA, which speeds up metabolism and helps with weight loss.
Meldonium was added to the World Anti-Doping Agency's list of banned substances on January 1.
Ten Russian sportsmen and women have been found to have taken meldonium, including tennis player Maria Sharapova, figure skater Yekaterina Bobrova, and speed skater Pavel Kulizhnikov.