Thomas suffered a torn triceps injury in the days before the Saints' preseason contest against the Houston Texans on Aug. 16 and surgery on the 6-foot, 335-pounder was necessary to repair the muscle.
Thomas began his career with Philadelphia in 1996 as an undrafted free agent from Northern Illinois.
"We were hoping to keep (Thomas) alive, but it really came down to having to get another body in here," Coach Sean Payton told the Times-Picayune newspaper. Thomas was kept on the active roster despite the injury for last Sunday's season-opener against the Tampa Bay Buccaneers.
Because of various injuries, he has played an entire 16-game season only six times in his career, including the 2007 season.
Thomas made 360 solo tackles in 154 games.