I think he'll be fine, he allegedly worked out to lose weight (although he doesn't look like Paris Hilton just yet...) over the winter to avoid some back problems and doesn't throw all that hard for a guy who's pretty big to begin with.
I also think that, unlike some of the other guys on the Cubs, he has seemed honest in the past, getting a cramp and you can see him shaking them off 'no big deal' on the mound but they shut him down anyway just in case. When Wood has shoulder soreness he keeps pitching even though he's not pitching effectively. Same w/ Prior. Too much 'I'm a gamer' going on.
In the game the other night, I think that the no-no caught up w/ him and he freaked out a bit. He had a 3-0 and a 3-1 count on two guys in a row but brought himself back in the counts by what appeared, at least on my TV while I was swilling beers w/ my jaw on the ground, to be focus and concentration, which have always been his biggest challenges.
The main problem is that if he keeps raking w/ the bat, Dusty's gonna have to get him in the lineup. Maybe he can C while Barrett's out?