Greece's Olympic 200 metres champion Costas Kenteris faces a disciplinary hearing that could bar him from the Athens Games after he missed a drugs test.
On the eve of the opening ceremony, the International Olympic Committee said it summoned Kenteris, the hosts' best medal hope and a national hero, after he and fellow sprinter Katarina Thanou failed to show for scheduled tests on Thursday.
Thanou, silver medallist in the 100 metres at Sydney four years ago, will also attend, said IOC President Jacques Rogge, who has ordered "zero tolerance" for drugs cheats in Athens.
"I have called for a disciplinary hearing into the Greek athletes. The process has started rolling," he told reporters.
It was not immediately clear when the hearing would be.
Kenteris's exclusion would be a national calamity in Greece.
But a senior Olympic official told Reuters that, if he had failed to turn up, he was a "fool" who "deserved" to be barred.
A Greek team spokesman said Kenteris and Thanou missed the tests on Thursday evening because team managers let them leave the Olympic Village before drug inspectors arrived.
The drama swept the Games city, with some young volunteers bursting into tears at the news Kenteris was under a cloud. Greek television broke into programmes to report developments.
"It seems he (Kenteris) didn't turn up for a test which, to me, is absolutely stupid," the Olympic official told Reuters on condition of anonymity.
"If he didn't turn up, he's a fool and he deserves to be out."
COMMUNICATIONS BREAKDOWN?
But a senior world athletics official said the pair seemed to have been victims of a breakdown in communication among Greek team officials and should therefore escape sanction.
"According to our information the Greek team leader was informed but not the athletes. To our mind this doesn't constitute a refusal," said Istvan Gyulai, secretary-general of the International Association of Athletics Federations (IAAF).
A missed drugs test is normally treated as a failed test and leads to immediate suspension from competition.
The Greek team said it had made a written appeal to the IOC to give the two athletes more time to undergo tests. Athens is the first Olympics at which a tough new, unified doping code has been in force.
A ban for Kenteris would be a sharp reverse for Greek hopes for a grand Games after a late spurt of impressive preparation and construction had silenced critics of Athens' sometimes chaotic build-up.
His standing among home fans has been likened to that of Australian runner Cathy Freeman at the Sydney Games.
Many had hoped that Kenteris, 31, would be given the honour of lighting the Olympic flame at Friday's opening ceremony.
It is not the first time that Kenteris, who rarely competes outside major championships, has been involved in controversy over regulations.
In March last year, the Greek authorities cautioned his coach Christos Tzekos for failing to tell them about a training trip Kenteris made to Qatar. Under IAAF regulations, athletes must tell the governing body of their whereabouts at all times.
Kenteris is the only man to win the Olympic, world and European 200 titles.
He first attracted attention in 2000 when he set a national record of 20.25 seconds, improving his time to 20.14 in Sydney then to 20.09 when he became the surprise winner before going on to take the world and then European titles.
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