McMichael broke his tibia and tore a ligament in his leg in the Rams' 31-14 loss to Buffalo on Sept. 28. On Monday, the team put him on injured reserve, ending his 2008 season.
Third-year player Joe Klopfenstein will start beginning with Sunday's game at Washington (4-1). Klopfenstein started as a rookie in 2006 before the Rams signed McMichael as a free agent.
The Rams expected big things of McMichael in 2008 after what essentially amounted to a lost season in 2007. Because of the many injuries to the offensive line, McMichael often found himself as a glorified third tackle as he stayed in to block instead of catching passes.
After finishing with a career-low 39 catches in 2007, McMichael led the Rams in receiving in the first week against Philadelphia and had 11 catches for 139 yards in four games.