John Glennon's afternoon update indicates that while Kevin Klein is likely to miss only one game after getting hit in the back of the head by Keith Tkachuk last night, Martin Erat is going to be out for a longer period of time, while they determine the extent of his injury:

The Erat issue is a little fuzzier. Erat was lim ping noti ceably today here in Columbus, and he's headed back to Nashville this evening for further reevaluation on Thursday. Doctors will be looking for things like torn ligaments, which would obviously be a worst-case scenario. At this point, however, Trotz is holding out hope that the injury isn't too severe.    

Erat went knee-to-knee with Barret Jackman late in the first period and didn't return. In the meantime, Mike Santorelli has been recalled from Milwaukee (along with Alexander Sulzer), and is probably going to get plugged into Erat's spot on the wing.

John Glennon discussed these developments on the Thom Abraham Show this afternoon, and you can listen to the update here (John Glennon on Thom Abraham Show 20091230).