The main route north from Montrose will stay closed to traffic for at least another two and a half weeks.
Lower North Water Bridge on the A92 was shut when Storm Babet struck.
There are fears the force of the floodwater could have weakened one of its central piers.
But a dive inspection is needed to fully ascertain the scale of any damage.
A lull in the storms at the start of the week gave a glimmer of hope the impact might become clearer.
But fresh rain brought by Storm Ciaran has kept the River North Esk level high.
An Aberdeenshire Council spokesperson said: “The Lower North Water Bridge on the A92 will now remain closed to all traffic until at least Monday November 20 on account of strong indications that there is undermining of one of the central piers.
“We’ve been unable to permit a dive inspection of the bridge owing to further heavy rainfall which continues to cause high and fast flowing water levels.
“We aim to commence inspections as soon as water levels and conditions allow.”
Problems for drivers have been exacerbated by damage to roads around Marykirk.
The A937 will also stay closed from Marykirk Bridge to Marymill farmhouse until at least November 9.
Details of road closures and diversions are available on the Aberdeenshire Council app.