The problem is he is never going to get the game-time to materialise into the average footballer we all know he could be.
However I do think buying another CM this window is a waste of time, because this season is already a write-off as far as the CL is concerned and we've got Lucas coming back, who has proven he's good enough, IMO, and Henderson and Shelvey needing game time. I'd sooner let them get some experience and buy a player with goals in them. I'd use the time from January onwards to allow them to adapt to the Premier League so they're ready for next year.
An established DM can be bought in the summer if needed.