Howard suffered a season-ending knee injury in Thursday's practice. He led the Bengals in tackles last season with 120 and had three tackles, one sack and one pass defensed Monday night against the Ravens.
Muckelroy is a third-year pro who was with the Bengals until being cut late in the preseason. He was a fourth-round pick by Cincinnati in 2010 and played in 14 games as a rookie.
- Roddrick Muckelroy