In the NFC Championship game, Sherman suffered ligament damage in his left shoulder. He didn't miss a play from practice and played the entire Super Bowl with the injury. During the game, he was making tackles and plays using his left arm.
The source indicated that the injury was worse than just an elbow sprain. Although the source didn't indicate the prognosis and timetable, it is likely he will go Tommy John surgery after the season.
Tommy John surgery is a procedure in which the ulnar collateral ligament (UCL) undergoes reconstruction using a tendon from elsewhere in the body.
Sherman injured his elbow in the NFC title game win over the Packers, but was fully practicing last week and insisted the left elbow would not be a factor in the Super Bowl.
"If I had to slap my brother, I'd be able to do it,'' he said jokingly on Thursday.
Sherman's girlfriend, Ashley, is expecting their first child (a boy) on Feb. 9. Ashley was in Arizona for the Super Bowl. Sherman said earlier this week they had a plan in place should Ashley go into labor during the game Sunday.
ESPN's Terry Blount and The Associated Press contributed to this report.