It's already been reported that Troy Polamalu and James Harrison are unlikely to play against the Oakland Raiders on Sunday, so it was no surprise they didn't practice on Wednesday. But in addition to being without those key players on defense, wide receivers Mike Wallace and Emmanuel Sanders were also sidelined.
Here's some analysis from Behind the Steel Curtain:
With it being early in the week, it isn't particularly troublesome, but these names appearing on the same report tomorrow would be more of a concern.
The wide receivers, Wallace and Sanders, would present the biggest problem. There are only four receivers on the roster (Antonio Brown and Jerricho Cotchery practiced, fortunately), and further absence from either one of them could alter the offense the Steelers have run most frequently this season (3WR, 1RB, 1TE).