Pettis (knee) was placed on injured reserve Saturday.
The move means little for the status of Pettis' sprained MCL -- he was already ruled out for Week 17 on Monday -- as the 49ers are just clearing roster space for healthy players prior to the season finale. The rookie second-round pick caught 27 passes for 467 yards and five touchdowns in 12 games, coming on strong towards the end of the season. Kendrick Bourne and Trent Taylor are likely to start at wide receiver Sunday against the Rams, with Marquise Goodwin (calf) also sidelined.