Repair work on the M4 in west London is progressing well and the motorway should open in the next few days, the Highways Agency said.
The repairs, which are taking place on the Boston Manor Viaduct just west of junction 2, were due to be completed on Thursday morning.
But the Highways Agency said the "complex" work is now expected to be completed within the next few days.
Motorists planning to travel into west London using the M4 were advised to continue using alternative routes via the M3 or M40 until further notice.
A Highways Agency spokesman said: "Complex work to repair cracks in the Boston Manor Viaduct on the M4 is progressing well but we are still in the critical phase of the works and the reopening of the motorway between junctions 2 and 3 will only take place when it is safe to do so."
The motorway, which is the main route from London to Heathrow Airport and the West of England, was initially closed between junctions 1 and 3 last Friday after a crack was found in a highly stressed part of the bridge supports. Work is now taking place to repair the crack.
The spokesman added: "Further finishing work will then be required before the road can be reopened." A diversion route is in place via the A4 and A312.
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 Olympic Games because it links London and the Olympic Park in Stratford with Heathrow.
The motorway will officially become part of the Olympic Route Network (ORN) on Monday, with one lane of 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 alterations.