Greek duo Kostas Kenteris and Katerina Thanou are facing expulsion from the Olympics after missing a drugs test.
The sprinters were unavailable for testing after being allowed to leave the Olympic Village by Greek officials to collect belongings from their homes.
Reigning 200m Olympic champion Kenteris and Thanou were then involved in a road accident and taken to hospital.
The pair had been ordered to appear before an IOC tribunal on Friday but have yet to leave their hospital wards.
Kenteris had been summoned to appear at 1030 BST, with Thanou half-an-hour later if deemed fit enough to travel.
But the pair have been told to stay in hospital for a further 48 hours and, as a result, have been given 72 hours to appear before an IOC hearing.
Hospital spokesman Christos Artinopoulos said: "Their condition is stable. They will remain in hospital for at least 48 more hours."
After an emergency meeting, IOC president Jacques Rogge ordered the launch of a three-man disciplinary committee, which includes former pole vaulter Sergei Bubka, to investigate the case.
Rogge said: "The IOC has launched a disciplinary hearing into these cases but I've no results yet.
"This is going to happen pretty soon. We will wait for the results and the executive board will then make a decision on that."
The news comes at the worst possible time for the host nation, just hours ahead of Friday's opening ceremony in Athens, where Kenteris was expected to light the Olympic Cauldron.
Kenteris was also a candidate to be Greece's flag-bearer in Friday's opening ceremony, but that honour will now go to weightlifter Pyrros Dimas.
Greek Olympic team spokesman, George Gakis, said: "They have been involved in an accident involving a motorcycle. They have been taken to hospital."
The spokesman added that the motorcycle accident happened near Glyfada, a southern Athens suburb where the Greek team has its training headquarters.
Greek athletics federation chief, Vassilis Sevastis, said: "As you will understand their psychological state was not good. It seems that it's not something very serious. Tests are ongoing."
A statement from Athens' main hospital said Kenteris had suffered cranial trauma, whiplash and leg wounds, while Thanou suffered abdominal bruises, injuries to the right hip and a muscular injury to her right upper leg.
Kenteris and Thanou, who won silver in the women's 100m at Sydney, were due to attend the drug test at 1930 local time on Thursday.
Christos Tzekos, coach of the two athletes, said they were at their home at the time of the test.
Having missed it, they apparently asked to take a test later in the evening at the clinic in the Olympic Village rather than at the anti-doping laboratory in Athens.
If they fail to have a plausible excuse for failing to take the random test, they face the prospect of being expelled from the Games and serving an automatic two-year ban.
Nick Davies, media director of the International Association of Athletics, said: "What will have to be decided [by the IOC] is if it was a no show - that is a surprise test which the athlete is unaware of.
"But a refusal, when an athlete does know, is a doping offence."
