From the Trib:
Wide receiver Santonio Holmes and center Sean Mahan did not practice Friday. Holmes had a death in the family, and he has been excused until Sunday. Mahan had some back discomfort. Quarterback Ben Roethlisberger suffered a slight groin pull during last night's practice. Free safety Anthony Smith tried to practice in the morning, but he could not finish because of a groin problem.
Now there's a surprise, Mahan with back discomfort. I guess so since he spends most of his time on his back.