The Gardiners Creek Trail underpass at Glenferrie Road, Kooyong, will be unexpectedly closed this weekend and all of next week.
Gardiners Creek Trail users will need to cross the road at the pedestrian crossing.
The detour is scheduled to come into effect from 10pm Friday.
The bridge is undergoing a $2.41M upgrade.
Initially it was thought that only the traffic lanes on Glenferrie Road would be impacted, however it has now been determined that riders on the trail could be exposed to safety risks.
Riders can still cross the bridge along Glenferrie Road using the footpath on the west side.
The upgrade includes: