American sprinter Marion Jones is at the centre of a new drugs controversy after her withdrawal from last night's Weltklasse meeting in Zurich.
Pierre Weiss, general secretary of the International Association of Athletics Federations, admitted there was "an option we cannot deny" that Jones may have failed a drug test.
Reports in the United States claim the 30-year-old has tested positive for EPO (erythropoietin), a blood-boosting hormone, however Jones has already stated her innocence through her lawyer.
The IAAF are aware of the reports, and will have been put in the picture should Jones have returned a positive sample.
Weiss told the BBC: "This is what everyone guesses - it is an option we cannot deny. For us, the situation is clear, an athlete is only positive once an A sample has tested positive and the contra-analysis of the B sample confirms this.
"This is not the situation at the moment. We are waiting reports regarding this case, which is why we cannot speak more.
"We have spoken with USTAF (United States Track and Field) but we are still waiting for what the contra-analysis tells us about this case."
Jones withdrew from yesterday's Golden League meeting, citing "personal reasons" for having to return home. Although that explanation would usually suffice in the case of an athlete withdrawing from competition, Weiss believes Jones could have been more open.
"We would have preferred that she stated what those personal reasons are. It would have made things more clear for the news media, the general public and the IAAF," he said.
Should Jones fail the drug test the 30-year-old could face a two-year ban. Jones has already stated her innocence through her lawyer.
Ther sprinter has been dogged by allegations of drug taking since winning five Olympic medals at the 2000 Sydney Olympics, particularly during the the Bay Area Laboratory Co-operative (BALCO) drugs scandal.
Jones, who won three gold medals in Sydney, may have previously been tainted by association.
Her former husband, shot putter CJ Hunter, retired after being found guilty of a drug offence in 2000, then Tim Montgomery, a former partner with whom she has a child, was also suspended last December.
Montgomery was involved in the BALCO investigation and apart from receiving a two-year ban, was also stripped of his world 100m record set in September 2003.
Widely regarded as the most accomplished sprinter since the late Florence Griffith Joyner, former basketball player Jones won both the 100metres and 200m in Sydney - plus a relay gold - and is also a double former world champion at the shorter sprint.
She was investigated by the United States Anti-Doping Agency when the whistle was blown about the designer drug THG, which resulted in Montgomery and many US leading athletes plus British sprinter Dwain Chambers suspended.