The Bears placed Johnson (thumb) on injured reserve Saturday.
Johnson popped up on Wednesday's injury report with a thumb injury. He ended up missing all three practices during the week before being ruled out from playing Sunday against Pittsburgh. With Johnson's placement on IR, he'll now miss at least three more games beyond Sunday, making his earliest return date Dec. 20 versus Green Bay. The Bears signed Brittain Brown to their 53-man roster from the practice squad Saturday to replace Johnson as the team's No. 3 running back.