The Frenchman was the world’s most expensive player until recently, but struggled to justify his price tag in his first Premier League season.
“I think he’s a top player, [but] I don’t know if he’s a player who completely makes a difference for Manchester United,” Moyes told ESPN.
“I think that over the years Manchester United have had players like Cantona, even Ryan Giggs, people who are special players.
“I don’t know if Pogba’s that. I think he’s a good player, I think he’ll add to Manchester United, but will he make the difference?
“Is he someone who will score the goal at really important stages in games or make the key pass? I’m not sure about that.
“But I do think that the machine that Manchester United are now, the size, the players they’ve got, you know they’ve got a massive stature to their team, I think Pogba adds to that.
“And I do think he’s a good player, but I’m not quite sure if he’ll make the difference in key games.”