Harrison is still recovering from knee surgery, and has yet to see any action in 2012. The Steelers do not know when he will be back.
Polamalu played in Week 1, and injured his calf. After sitting out last week, he has still not returned to practice.
The Steelers will also be without running back Rashard Mendenhall for the third straight week. Mendenhall was a full participant in practice this week, but the Steelers are being cautious with his return.
The Steelers may not consider the Raiders to be too much of a threat, and with a Week 4 bye, they may just be getting their players extra rest.
This story was originally published on SBNation.com