Aye, the problem is that we've already got two preferred deep lying central midfielders. Allen's been impeccable for the most part this season, and Gerrard's Gerrard, which means he's undroppable when he's fit. The problem with dropping Gerrard is also his ability to play a killer ball at any moment, even if he's having an off game. Factor in the return of Lucas, who's an automatic starter as the man behind the back four and you see the dilemma for Sahin.
Not only that, but in the times he's been given a place in the team he hasn't looked as impressive as the likes of Henderson, and Shelvey, who're both young players pushing on in their careers.
I'd love him to take his chance and play like he did at Dortmund, but thus far he's struggled with the pace of the game. He's also looked really lightweight, and fragile, which hasn't been something we can afford whilst Lucas was out.