Gresham is scheduled for surgery on Thurdsay after being diagnosed with a herniated disc, NFL Media Insider Ian Rapoport reports, via a source informed of the player's situation.
At this point, per Rapoport, there is no firm timetable for Gresham's return to football activities. More will be known after the procedure.
The back injury was discovered in the free-agent process, Rapoport reported last week.
Gresham had entered into contract talks with the Raiders by then. If the team's doctors discovered the injury, it's the second time in two years that a potential signing was overturned by a failed physical. The Raidersbacked out of a contract with offensive lineman Rodger Saffold after tests revealed a shoulder injury last March.