To me he seems like he's physically a level above the rest. There's players who can run a lot but Hakan's explosiveness, tackling, aerial ability, excecuting things with the ball and so on, that makes him unreal. These things mentioned take extra energy out of you, especially when you have to destribute the ball constantly around as you're the organizator, at the same time you have to sprint back and win the ball.
We are surely fucked if he picks up a long term injury. It doesn't seem like it, but you never know with football.