Bengals safety Reggie Nelson went low at Bell's leg after making a first-down catch. Dri Archer came in to replace Bell, who jogged off the field. Archer made a catch on his second play in the game.
Bell was seen getting his knee examined on the sideline after the hit.
The Steelers essentially have no depth at the running back position, and Bell's absence would hugely and negatively affect the Steelers' offense - the same group that topped the franchise's single-season scoring mark in the first quarter of their game against Cincinnati.
Bell was named the team's MVP after breaking the team's single season yards from scrimmage mark.
Ben Roethlisberger threw his first interception in four games on the drive after Bell left.