Battle Road between Windsor Road and the Asda supermarket is currently shut to traffic due to major sewer repair works.
Southern Water said the firm is repairing a collapsed sewer in the middle of the road.
It said it was unable to find the exact location of this until recently and initially believed it was a private issue which resulted in a delay in starting repair work.
The company said the reason why the works are taking so long is because engineers will have to dig deeper into the road than previously thought and they have to modify the dig area to allow for them to carry out work in a deeper location than expected.
A Southern Water spokesperson said: “We’re sorry for the disruption our work to repair a collapsed sewer is causing in Battle Road, St Leonards.
“The repair is much more complex than we had anticipated and we have had to adapt our work to do a deeper dig to repair the sewer. This will take some time and we’re sorry for the continued inconvenience this is causing.”
A diversion is currently in place.
Southern Water said the works are expected to be completed, with the road reopened by February 4.
It is not the first time Battle Road has had to close for an extended period of time.
The section of road was partially closed between March 2021 and earlier last year, due to the Battle Road arches having to be demolished.
Temporary concrete protection blocks were installed as part of the demolition works. The steps from Battle Road up to the rear of the properties on Silverlands Road were also permanently closed.