Cristiano Ronaldo's return to Manchester United has already had a positive effect on the mentality in the dressing room, according to defender Luke Shaw.

The Portugal international is the club's leading scorer with five goals in six matches since re-signing this summer.

And while United have had a mixed start to the season, losing to Young Boys in the Champions League, Aston Villa in the Premier League and West Ham in the Carabao Cup, Shaw insists Ronaldo's presence has been a positive one.

"You know the star he is, what he has been doing over a number of years, it is just unbelievable to be in a dressing room with him," Shaw told BBC Radio 5 Live.

"You see the way he conducts himself, how professional he is. It's clear to me why he has been at the top for so many years.

"His mentality is second to none. I think he has really improved that in and around the changing room."