Lyudmila Blonska, the Ukrainian athlete who won silver in the women's heptathlon, is facing disciplinary action after failing a drugs test.
It is understood Blonska, who has already previously served a two-year ban for drugs, tested positive for an anabolic steroid.
The case is expected to come before the IOC's disciplinary commission and executive board, which meet tomorrow.
After Blonska's silver medal Britain's Kelly Sotherton, who finished fifth in the event, called for a worldwide policy to prevent drug cheats from returning to compete in the Olympics.
The IOC refused to confirm the positive finding, saying in a statement: "The IOC does not comment, or provide information, on any doping cases until a decision is made by either the disciplinary commission or executive board."
Blonska, 30, was given a two-year ban in 2003 after testing positive for steroids. If the latest positive test is confirmed by the IOC tomorrow then she could be given a lifetime ban.
Sotherton said early this week: "I'm not happy she competed again. We have rules in our country that we abide by. We don't bring anybody who cheated previously, so why should any other country?
"I'd have been really upset if she'd won gold. The penalty you should pay if you take drugs is not to compete at the Olympics."
Under usual IOC procedure, Blonska will be stripped of her silver medal and her accreditation for the Games withdrawn. It would mean the USA's Hyleas Fountain moving up to silver, Russia's Tatiana Chernova moving up to bronze, and Sotherton's official finishing position being fourth.