Chicago Bears RB Matt Forte didn't get involved in a single practice all week due to his sprained right ankle, and won't play in Sunday's game against the St. Louis Rams.Coach Lovie Smith made it official Friday by ruling Forte out. 

"No doubt, we feel comfortable with (backup) Michael Bush," Smith said.
Smith said both Armando Allen and Kahlil Bell are ready to go as backups in case Bush suffered an injury.

Forte went out in the third quarter of the Sept. 13 game at Green Bay. He has 111 yards on 23 carries to go with seven catches for 89 yards after signing a $32 million, four-year contract in July. Forte missed the final four starts last season with a knee sprain.

Bush, signed in free agency for $14 million over four years after a big season replacing Darren McFadden with Oakland, has rushed for 96 yards on 26 attempts. He'll bring more punch, especially in short yardage situations, but is not the breakaway threat Forte supplied.

Bell and Allen both played late last season after Forte's knee sprain. Bell had been cut by the Bears in preseason for refusing to take a $500,000 pay cut, but returned for the league minimum of $615,000 after Forte's injury.

The Bears Sunday at Soldier Field face a Rams defense ranked 21st in the league against the run.

Follow Bears reporter Gene Chamberlain on Twitter @CBSBears.