Well the thing is that Griezemann would be a fantastic signing but if the midfield cannot hold the ball and provides forward passes, they won't score... Our best midfield right now is more or less Herrera Schneiderlin Mata, maybe Rooney (if remotivated by Mourinho). Pogba could replace Herrera in games where we need more physical impact... Or play instead of Schneiderlin if we want to dominate a weaker side. I don't feel like he's the player who's going to change everything, but he would bring a Vieira type of influence, i.e. he could be the next Roy Keane. And I would love to see him combine with Herrera and Mata.