I'm going to have to back track a bit on Juan. I am now leaning toward the opinion that we can't be a top team and have Juan in the lineup any more than a bit role. He doesn't pressure the ball at all and the top of the defense, it's him and Lukaku or Sanchez that would need to begin the pressure in order to force a back pass or a long ball... otherwise, teams simply possess against us like Liverpool did.
I believe that when we have the players, and for the most part I believe we do have these types of players now, we can press 3/4 up the field and then everyone cover the easiest passes to force the opponent to give the ball away via a long ball or back pass to the goalie with a long ball to follow. Without 100% buy-in, pressing doesn't work and Mata is either coached to not press or he's just not willing to do so which puts us at a disadvantage.
I've watched this closely over the last year as our "style" has come into question, and there were many games, maybe more than half last season where we do press and aggressively force turnovers, playing fast and aggressively after we win the ball but enough times we get a 2-0 lead and stop or we play a team that's a bit better in possession and we tend to be too conservative defensively. THIS IS MY # ONE/Main concern. We have the athletes on the wings and in the middle of the pitch to press/fight/win possession. Our players are fast, strong and frankly most of them aggressive enough to be coached into this philosophy but Jose tends to revert to a more sagging approach later in games.
All of that said, I unfortunately don't think Juan can play a starting role in a team that plays in this fashion. I think he's our most creative player (along with Pogba) but he's a real liability in defense.