The reportedly have released receiver after just three games with the team, according to Ian Rapoport of NFL Network.
The 31-year-old had just one catch for nine yards after joining the team in mid-September. He was limited to seven snaps in Sunday's game against the Philadelphia Eagles with receivers Brandon Aiyuk and Deebo Samuel now healthy after dealing with injuries earlier in the year.
Tight end George Kittle also played in Week 4, giving the 49ers several quality pass-catchers after being extremely thin in this area when they signed Sanu.
This article will be updated to provide more information on this story as it becomes available.