Greece's defending Olympic 400m hurdles champion Fania Halkia has tested positive for banned drugs. Halkia, 29, is understood to have tested positive for a steroid after officials from the World Anti-Doping Agency (Wada) visited a training venue in Tokyo last week.
An IOC spokeswoman said: "Fania Halkia failed a pre-competition test conducted in Japan by Wada during the period of the Games. It was an IOC test done on our behalf by Wada as it outside Beijing.
"A disciplinary commission will now convene to discuss the case and it will then go to the IOC's executive board for a final decision."
Halkia is thought to have left Beijing and returned to Greece after being informed of the positive finding. The hurdler faced a barrage of questions in Athens after a startling improvement saw her come from being a virtual unknown to win gold.
"Why do people want to give a negative impression of sports?" Halkia said then.
The latest positive test underlines Greece's problem with drugs in sport — Halkia is the 15th Greek athlete in the last three months to fail a doping test.
Tassos Gousis, a 29-year-old 200m sprinter, tested positive for the banned steroid methyltrienolone just before going to the team's Olympic training camp.
Greece have already had 11 weightlifters, a boxer and swimmer Yiannis Drymonakos withdrawn after positive tests in the past three months.
The IOC's executive board has also ruled sprinter Katerina Thanou ineligible for the Games.
The Sydney 100m silver medallist withdrew from Athens following a missed drugs test and was banned until December 2006. She qualified for Beijing but required IOC approval to compete in Beijing.