For a couple of months, I don't think playing center will hurt Z appreciably more than playing wing outside of a freak injury. Aside from his back, which is supposed to be "fixed," has Z had any other significant recurring injuries?
Nothing negative has been reported about Zetterberg back after the surgery. It was 1,5 years ago.
I just think that his back rehab killed his normal summer training at last summer and he was out of full physical condition for later part of the season. Just was worn out. NO energy, skating was off, and nothing was reported that his back causes these problems. It was just something "general". That's out of physical condition for me. And there's games so heck of amount during the regular season, that you can't much train between them, just play through.
Now, if he has completed his normal summer training program, I think he could return on his normal form again, and will have a better season.