Athens organisers have again postponed the installation of a huge steel dome above the main stadium just 101 days before the Olympics' opening ceremony.
Government officials had said the sliding into position of the roof would take place at the weekend, but contractors say more time is needed to prepare for the final assembly.
The operation is now expected to start on Friday at the earliest and there is little room for further delay.
The International Olympic Committee has said that if the two arches are not in place by May 20th, the €150 million project, intended to be the Games' architectural centrepiece, would have to be scrapped due to time constraints.
The roof is the biggest concern for organisers who have repeatedly shifted the date to slide the huge arches, which will carry the 18,000-tonne steel roof.
Construction on the roof is hampering landscaping work around the Olympic complex ahead of the August 13th-29th Games which have been dogged by concerns over whether venues will be ready in time.
"The slide will begin around Friday or the weekend and not earlier," a main contractor said. "We are still cleaning up around the site to make sure that everything is in place before we move the arches."
Spread across the stadium like a spider's web with its translucent blue panels "lighting up the night", the roof is seen by architects as a huge engineering challenge.
"Everything will go well but the slide, which will last for about two or three days, must be very precise," the contractor said.