Urgent repairs are needed to Ballagawne Bridge near Kirk Michael.
The Department of Transport has discovered corrosion on the iron girders which support the structure, on the Kirk Michel to Peel Road.
No major work has been carried out on the bridge since it was built, to carry traffic over the old Kirk Michel to St John's railway line.
Extra supports will be installed on either side over the next two weeks, with traffic directed over the centre of the bridge to avoid the weakened area.
"He enjoyed hearing the Manx national anthem!": King greets guests at Government House
His Majesty meets representatives of the Manx community at Garden Party
Crowds gathered in glorious sunshine to see the Monarch
Live blog: King Charles visits the Isle of Man
Updates from the Lord of Mann's first visit to the Island since ascending to the throne
King speaks of Island's 'enduring partnership' with the crown
King Charles III spoke in Tynwald this lunchtime