A section of the London South Circular is to remain shut for two weeks while emergency work to rebuild a sewer is carried out.
The structure, which runs below London Road near Sainsbury's in Forest Hill, collapsed on Friday night.
A Thames Water spokesman said assessments had been undertaken and rebuilding work would take place over the next two weeks.
The road is closed both ways between Sydenham Hill and Dartmouth Road.
The spokesman said a diversion was in place but drivers should expect some disruption.
He said: "The rebuild of this section of sewer is expected to take about two weeks.
"We are really sorry for the inconvenience this is causing road-users."
The Horniman Museum and Gardens is on the stretch of London Road affected by the closure.