Work by Scottish Water to repair sewers on Ingram Street should have begun on September 23 and been completed on September 27.
But the company said yesterday that "engineering difficulties" mean it is now unclear when the work will be finished.
Ingram Street will be closed westbound from High Street to Albion Street and motorists are warned to expect delays.
Diversions are in place southbound along Bell Street and Albion Street.
Northbound diversions travel along George Street and Montrose Street.