Don't expect Pogba fireworks, says Man United boss Mourin...
"So maybe it's not an 'impact', maybe it's just a natural improvement of the team, because he's a super football player."
Pogba, who left United in 2012, scored 34 goals in his four years at Juventus -- an average of 8.5 per season.
On the chances of him reaching Ronaldo and Messi's level, Mourinho said: "First of all, when you speak about the best players in the world, you go immediately to the ones that score a lot of goals.
"You don't give a Golden Ball to a goalkeeper. You gave a Golden Ball to (Fabio) Cannavaro once, but because in that season he was the captain of Italy, the world champions, and there were not many (other) top players.
"(Paolo) Maldini never got a Golden Ball. (Javier) Zanetti never got a Golden Ball. Top goalkeepers over history didn't get a Golden Ball, so you look immediately to the ones that score a lot of goals.