The M4 motorway in west London will not reopen on Thursday morning, the Highways Agency said.
The motorway, which is the main route from London to Heathrow Airport and the west of England, will remain closed between junctions two and three due to continuing repair works to the Boston Manor Viaduct, just west of M4 junction two.
The Highways Agency said 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".
Drivers planning to travel into west London via the M4 are advised to continue using alternative routes via the M3 or M40, the Highways Agency said.
The AA's head of public affairs Paul Watters has said the timing of the closure was "shocking" with less than a month to go until London 2012.
"It’s a close shave, the timing is shocking with the Olympics so close. I expect the Highways Agency are quite nervous about it. We just hope it is fixed by Thursday, because it is the most vital artery," he told the Daily Mail.