People keep bringing up Pavard in the middle, clearly don't get our system; it is not the same role as a cover CB(last man) in a 2 CB system; nor is it the traditional sweeper in old days 3 backs (which is also one of the weakness of the old back 3, holes to land cross ball without offside and not strong enough to compete ariel there), cause we are playing 2 semi CBs on the side not 2 full time CB like back 4; also Hakan is our dmf, it works more like the stopper in back 4 on the first contact on direct balls.
We need someone who more classical no bullshit tall strong CB as our mid CB, think Blanc, Stam, Vidic, Matrix, Acerbi, one of the key elements is stop direct ariel long passes this role cannot function without this.
If Bisseck is good enough in the defense, he can play that role, but he is not there yet, luckily he is playing a role that is more forgiving in defensive mistakes, which also allows him to recover, however, if he gets better at the basics and be more determined on not letting the ball pass him in any sense, he will be a good candidate, but right now, it is a disaster waiting to be happened, if you put him in there.
Not to mention, there are other differences in positioning and ball playing, and the decision when to contest is also difference, which is why Bastoni isn't exactly a mid CB.