Backup quarterback Charlie Batch -- making his first start since early in the 2010 season -- will play in place of Roethlisberger.
Roethlisberger suffered a high ankle sprain during a win over the Browns and then gritted his way through last Monday's loss to the San Francisco 49ers, a performance in which it was evident the injury limited the Steelers quarterback's ability to make plays. Roethlisberger threw three interceptions that night and was noticeably hobbled as the Steelers failed to score a touchdown for the first time this season.
Roethlisberger said Wednesday he would prefer to play and believed his ankle was in pretty good shape after Monday's game. Yet he watched both practices this week in sweat pants as Batch took the snaps with the first team.
Roethlisberger last missed a start due to injury in 2009, when a concussion forced him to sit out a loss to Baltimore.
NFL Network insider Jason La Canfora reported Wednesday that team sources said Roethlisberger is likely to sit out the final two games of the regular season. La Canfora reported that Steelers offensive coordinator Bruce Arians preferred Batch as a replacement for Roethlisberger over Dennis Dixon, whom others in the organization believe is a more viable starter because of his athleticism and improvisational skills.
Should Batch struggle and become a sitting target behind a wounded offensive line, Dixon might see the field Saturday.
The Rams have their own quarterback issues. Sam Bradford continues to be slowed by an ankle injury that kept him out of practice this week and is listed as doubtful. Backup A.J. Feely has been ruled out again, meaning Kellen Clemens is likely to get his second straight start.
The Associated Press contributed to this report.