The structure was damaged by an overturning lorry leaving a section of concrete hanging over the motorway.
The route was closed following the incident last night.
The Agency said: “The closure has resulted from an incident on the link road from the southbound M6 onto the westbound M55 at around 7.30pm this evening (Wednesday 12 February) when a lorry overturned in gales – damaging the link road bridge where it crosses over the southbound M6.
“The damage to the bridge needs to be fully inspected and repaired. It is unsafe to do the work until gale force winds have subsided.
“A section of concrete is hanging over the southbound carriageway of the M6 and it is not possible for either the link road or southbound M6 to remain open until the repairs are effected – possibly after the morning’s peak travel period.”