Keisel tore his triceps on Sunday in a loss to the New Orleans Saints. After the game, safety Mike Mitchell said, "It almost makes you want to cry when you lose a player like that because he's so instrumental to who we are and what we try to do here."
A 13-year NFL veteran, Keisel has spent his entire career in Pittsburgh. He played in all 12 of the Steelers games so far, making four starts and 17 tackles and grabbing an interception.
The Steelers signed defensive end Clifton Geathers to replace Keisel. Geathers was a sixth-round draft pick in 2010 and has played 37 games in his career.
Pittsburgh (7-5) plays the Bengals (8-3-1) in Cincinnati on Sunday.
- Molly Geary