The M4 motorway in west London remained closed today with officials admitting delayed repair works on a damaged flyover could continue into the weekend.
The works, which are taking place on the Boston Manor Viaduct, just west of M4 junction two, were due to be completed this morning.
But the Highways Agency said the final repairs had reached a "critical stage" and "due to the complexity of the operation more time than originally envisaged is required to complete the work safely".
It said that the road will now reopen "within the next few days".
The motorway, which is the main route from London to Heathrow Airport and the west of England, was initially closed on Friday between junctions one and three after a crack was found in a highly stressed zone over bridge supports. It is currently shut between junctions two and three.
Drivers planning to travel into west London via the M4 are advised to continue using alternative routes via the M3 or M40.
Roads Minister Mike Penning said: "I share the frustration of motorists at the continued delay to the opening of the M4.
"However, let's be absolutely clear, safety must be paramount and I will not allow the road to be reopened until this repair work has been completed successfully. This is a very complex operation and it is not possible to predict precisely how long it will take.
"I want to thank motorists for their patience and assure them that we are doing everything we possibly can to fix this problem and get the road safely reopened as soon as possible."
The M4 is expected to be one of the busiest routes during the Games because it links London and the Olympic Park in Stratford with Heathrow.
The motorway will officially become part of the Olympic Route Network on Monday, with one lane on each carriageway reserved for competitors, officials and sponsors.
Drivers have been warned the ORN will include temporary changes including suspended turns, stopping and loading restrictions and traffic signal timing alterations.
AA president Edmund King said: "It is obviously frustrating for thousands of drivers that the M4 remains closed but most people realise that this is a necessity.
"I have been briefed personally by the Transport Secretary (Justine Greening) on the situation and have been assured that the Highways Agency is doing its utmost to make the road safe."
He went on: "The fact that the road is elevated adds to the danger not only for the road users but also for those below.
"We hope that this road to nowhere is re-opened soon as the clock is counting down with just four days to go before this road is to be designated part of the Olympic Route Network."
Shadow transport minister John Woodcock said: "We are now just days from the continued closure of the M4 becoming a national embarrassment for Britain in the run-up to the Olympic Games.
"Ministers must explain why we are on the brink of humiliation when major issues with this bridge were uncovered months ago.
"Can ministers guarantee the M4 will be open in time for the start of the official Games period on Monday? If not, what is their Plan B?"
Downing Street said it was exploring of range of back-up plan options to put in place if the motorway is still closed on Monday when athletes and officials begin to arrive, but refused to say if they included opening a single lane for Olympic traffic or using the Heathrow Express.
David Cameron is receiving regular progress updates and Highways Agency officials have again said they expect work to be completed in the "next few days".
The Prime Minister's spokesman said: "There are contingency plans to ensure that athletes and the Games family arriving at Heathrow can get through easily."