Athletes who tested positive for meldonium before March 1 could have bans overturned less than four months before the Rio Olympics after WADA said it was unable to establish how quickly the drug, outlawed since January 1, cleared the human body.

The World Anti-Doping Agency's notice to national anti-doping bodies is expected to have a major impact on many of the 172 athletes who have tested positive for the performance-boosting drug since January.

They include five-times grand slam tennis champion Maria Sharapova, who was among 40 Russian athletes to test positive for the drug after it was added to WADA's list of banned substances in January.

Sharapova's lawyer John Haggerty said on Wednesday that WADA handled the issue "poorly" and was now trying to make up for it.