Sculcoates Bridge will remain closed to motorists until further notice.
A three-day inspection has identified a number of issues with the structure, which now needs urgently repairing.
Peter Curry, structures, safety and emergency planning manager for Streetscene, said: “We had hoped to get the bridge repaired and open to commuters by Friday morning, however following a thorough inspection, the condition is deemed to be far worse than we originally expected.
“We will be undertaking these critical works as a matter of urgency before reopening the bridge to the public.”
The diversion route for motorists will continue to be via North Bridge.
Pete said: “We apologise for any disruption caused and thank motorists for their patience whilst we carry out these vital works.”