Antoine Bethea will miss the remainder of the season with a torn pectoral muscle.
In seven games, Bethea had recorded 32 tackles and a sack for San Francisco. Rookie Jaquiski Tartt is expected to make the start in place of Bethea.
The 49ers defense takes a hit with the absence of the three-time Pro Bowler as San Francisco has struggled this year by ranking 20th in points allowed per game and 30th in both passing defense and overall defense.
The team has activated Jerome Simpson, who missed the first six games of the year after being arrested in July 2014 on a misdemeanor charge for having marijuana and an open bottle of alcohol in his car while driving with a restricted license. The incident marked his third arrest. He did not play last season.
- Christopher Chavez