Athens - Track's governing body began investigating on Thursday whether two Greek sprinters who withdrew from the Olympics had tried repeatedly to avoid doping testers.
While the International Association of Athletics Federations investigates, Kostas Kenteris and Katerina Thanou are free to participate in competitions.
The two national sports heroes who won gold medals at the Sydney Olympics have denied wrongdoing.
And their lawyer, Michalis Dimitrakopoulos, said of the latest probe: "We have nothing to fear."
Under IAAF rules, athletes face sanctions in the event of three drug-test "no-shows" in 18 months.
Prior to the missed test in Athens, the Greek runners were absent when testers looked for them in Chicago on August 10 and 11.
The IAAF is also looking into a third possible case involving Kenteris in Tel Aviv, Israel, in late July.
The IAAF's doping inquiry board will gather all information about the case.
If there is sufficient evidence of missed tests, the case will go the Greek athletics federation, Segas, which will conduct a hearing.
The IAAF can reject a finding by the federation.
"It will take weeks, but hopefully not months," said IAAF spokesperson Nick Davies.
Prosecutors are also investigating whether Kenteris and Thanou were deliberately trying to avoid drug tests, as well as the circumstances surrounding a suspicious motorcycle accident on the eve of the games.
Kenteris, the surprise 200-metre gold medallist in 2000, and Thanou, who took silver in the 100 metres in Sydney, could not be found at the Olympic Village for an August 12 drug test.
Hours later, they said they were involved in a motorcycle accident that happened because they were rushing back to the Olympic village to be tested.
They spent several days in the hospital with cuts and bruises, and later withdrew from the Olympics.
"All information obtained by Greek authorities will be looked at," Davies said.
As part of the government probe, fraud inspectors with Greece's Finance Ministry searched the offices of the sprinters' coach, Christos Tsekos, for six hours on Monday, seizing documents and computers from his food supplements company in Athens.
Last week, inspectors from Greece's National Organisation of Medicines raided the offices and a warehouse, and confiscated some items that they said contained small amounts of anabolic steroids.
In another development, a man who said he witnessed the motorcycle accident involving Kenteris and Thanou was sentenced to 14 months' imprisonment for fraud and jailed in Athens' Korydallos prison.
The man, Meletis Zografos, had been convicted in absentia four years ago for pretending to be a lawyer.
At least two people, including Zografos, have told police they witnessed the accident - including one man who said he drove the two athletes to the hospital.