No, he can't. He's not a box to box midfielder. He generally plays in a more advanced role like a #10 or the lead attacking midfielder in a midfield 3 which is Bruno's role, not Pogba's. Something Pogba can do, but not something he's asked to do when he is playing with Bruno in front of him. Grealish is in no way a suitable Pogba replacement for this formation, and there are few formations the would work with Grealish, Sancho, Martial, Bruno, and Greenwood all playing outside of a 4-2-3-1 with Grealish being the left-attacking midfielder. But, that's probably a strategy to use at home vs weaker opposition, and in that scenario, he's a replacement for Rashford, not Pogba.