Alan Robinson of the Pittsburgh Tribune-Review reported both players sat out Thursday's sessions. Neither is expected to play against the Oakland Raiders on Sunday, according to Sporting News.
Polamalu missed his fifth consecutive practice with a calf injury, and Harrison has been sidelined for weeks with discomfort in his knee. The Steelers didn't need either player to subdue the New York Jets in Week 2, and the Raiders, on paper, loom as one of Pittsburgh's less nettlesome opponents early in the season.
We know this about the Steelers: Few teams do a better job of getting their reserves ready for action.
Follow Marc Sessler on Twitter @MarcSesslerNFL.