And as the article I linked to noted--they don't know the extent of the injury yet--a projection of time missed within an hour or two after the game is a bit rare, and even more rare for a prime-time game. Polamalu hasn't been looked at carefully yet.
Keyshawn Johnson was on ESPN saying that Dick LeBeau is too good of a defensive coordinator to let this affect the Pittsburgh defense too much. While I'm sure Dick isn't hiding under a desk somewhere, whispering, "I don't know what to do. I just don't know. what. to. do.", he's not chomping at the bit to redesign his defense without the best all-around safety in the game. And he's going to have to.
Evidence of that? Look at the first quarter, when the Titans were backed up and Chris Johnson looked like he had found some space to run in forward towards--Polamalu flew in and shut it down--HARD. Or look at his one-handed interception later on. Dick LeBeau's defense just got a bit more predictable, a lot less explosive, and a lot less experienced.
Look for 3 to 6 weeks of opposing teams testing that secondary down the middle, and maybe single back sets with two TE's, seeing if one can run on the Steelers now.