Didn't really watch much of him at Celtic, but I thought I started to hear mentioned less and less in the second half the season. I remember watching the Celtic v Rangers cup game thinking it was odd he wasn't playing. But from you've said it makes sense now.
I'll also be intrigued with where he will go. Given his previous success in Holland, lack of success in the Prem (City/Stoke) and mixed experience in Scotland I wonder whether he might go back to a European league where it might be a little less physical or where he might get more time on the ball.