Sanu was released by the New England Patriots in September as part of the team's cuts ahead of the 2020 season. It capped a disappointing run with the team after he was acquired in a 2019 deadline trade in exchange for a second-round pick.
He finished with 26 catches for 207 yards and one touchdown in eight games, failing to provide the Patriots with the much-needed receiving threat they were seeking for the stretch run.
Sanu finished 2018 with a career-high 838 receiving yards and was off to a strong start in 2019 before being traded, catching 33 passes for 313 yards in seven games. His 4.7 receptions per game were his highest rate in the NFL.
Though he was forced to undergo surgery on his ankle in the offseason, his trainer, Hilton Alexander, was encouraged by the recovery.
"I would tell you he's probably faster, quicker, leaner and in better shape now than prior to the surgery," Alexander said, per Mike Reiss of ESPN. "I would say he's way ahead of any doctor's knowledge or prediction where he would have been at this point. Way ahead of the curve."
Sanu will now get a chance to prove he can still contribute after landing a deal with the Niners, who have already battled through injuries at the wide receiver position this season. Sanu should also hit the ground running in San Francisco's offense, having played under head coach Mike Shanahan when he was the offensive coordinator in Atlanta.
The team has other options at wideout, but the latest addition should see plenty of snaps going forward in 2020 while players like Brandon Aiyuk, Deebo Samuel and Richie James recover from injuries.