Mike Tomlin said Tuesday that linebacker James Harrison suffered a fractured orbital bone that will cause him to miss the next several weeks.
Harrison will have surgery Wednesday.
With linebacker Jason Worilds doubtful to play Sunday against Tennessee, Lawrence Timmons will shift outside, with Larry Foote starting inside.
On the positive side, Tomlin said he expects quarterback Ben Roethlisberger to play, though he'll obviously be limited early in the week.
Tomlin also expects Brett Keisel, Doug Legursky and Jonathan Scott back in the lineup this week.
The return of Keisel would be particularly helpful, considering Aaron Smith is doubtful to play Sunday.
The Steelers are also hurting at running back. Mewelde Moore has a sprained ankle, while Rashard Mendenhall has a hamstring strain, though Mendenhall is far more likely to play than Moore.
All in all, it's a long list of injuries.