St. Louis, MO -- (Sports Network) - St. Louis Rams running back Steven Jackson will not play Sunday against the Chicago Bears because of a strained right thigh muscle.

Jackson was hurt during the October 19 game against Dallas, despite rushing for 160 yards and three touchdowns, and has now missed four of the Rams' last five games.

"I have been staying with the game plans and preparing myself as if I am going to play Sunday," said Jackson. "I have been doing that for the last three or four games that I have missed. Mentally, I am still sharp and I just want to be able to get a full week of practice for (Coach) Haslett and go from there in the last five games."

For the season, Jackson has 525 yards on 128 carries with four touchdowns and added 25 catches for 259 yards.

Antonio Pittman, who has rushed for 224 yards on 57 carries and gained 80 yards on 13 catches this season, and Kenneth Darby, who has totaled 141 all- purpose yards this season, will likely see the majority of carries out of the backfield in Jackson's absence.