Kalidou Koulibaly - He would be a good replacement for the aging Vinny and Otemendi. I think he would make our starting line up too, alongside Laporte. He was impressive in games against Liverpool and PSG. Very quick, good positional play, reads the game well and he is good going forward. Ferland Mendy - Looks like a decent left back, very quick and skilful going forward, played very well against us, and could compete with Benjamin. In the next few of years this would mean we have two good right backs, two good left backs, and three good center backs all competing. If you count Vinny and Otemendi leaving in the next season or two. Marco Veratti - Would cost a packet but he could possibly replace Dinho or David Silva. He's very good defensively and even better going forward. He retains the ball well, and can control the game in a similar manner to how Pirlo did it in that deep lying role. He can transition between attacking midfield and defensive midfield well. Adrien Rabbiot - He is similar to Verrati in his style of play and would be a good alternative or even compliment him. Currently we have 5 midfielders, who if all fit could start a big game. Dinho, David Silva, Gundogan, KDB and Bernardo. Realistically, you could narrow that to 4, as you wouldn't want Gundogan starting ahead of any of the others in a big game. Now, the first two don't have many more years left in them, and Gundogan could be upgraded. So with these two signing we get defensive players who can also play forward. Meaning Verrati, Rabiot, KDB and Bernardo to pick from. With these players, you could either player 1 or 2 deep midfielders and not compromise on attack.