Spillane (back) has been ruled inactive for Monday's game against the Colts.
Spillane popped up with a back injury Friday and was a limited participant in the Steelers' final two practices of Week 12 prep. While it's unclear how this issue first arose, the 26-year-old will miss his first game of the season. Over 10 games, Spillane has recorded 40 tackles, one sack and four passes defended while primarily playing as a backup inside linebacker. His absence could leave Marcus Allen and Mark Robinson to play increased roles behind starters Devin Bush and Myles Jack on Monday.