Grealish is reported to be keen on moving to Old Trafford this summer.
"He's the main player at Aston Villa and we can all see what he does, if he goes to United where Pogba, Martial, Rashford are the main players, will he have that much of an impact?
"To say that because he's at Manchester United he's going to play for England, that's what he has to prove. He's the main man at Aston Villa, he does everything and everything comes through him, that's why he's got such a big profile and why he plays well. If he goes to Manchester United, is he going to take over from Pogba or Fernandes as the main playmaker, probably not.
"So then just because he's at Manchester United it doesn't mean it will help his England chances. His England chances are great because he's playing well at Aston Villa, he has to make that decision and his decision can't be based on whether it is going to help his England career, his decision has to be based on whether this is going to help his football career because he'll be at a club in the Champions League or fighting for honours."