The pair have played together internationally for Portugal for several years.
"I think [Fernandes] he is going to adapt [to the Premier League], he has already played in Italy when he was younger, so it's not his first experience abroad," Bernardo told Sky Sports.
"I'm happy for him, I'm happy that he's playing for one of the biggest clubs in the world and I think he's going to do great at Man Utd.
"The best thing about Bruno is his mentality and the way he gives himself to the team 100 per cent and he just goes in every game. It doesn't matter who he's playing against and his mentality and character is the best thing about him.
"The first time I played with Bruno, we were 18 years old so my first game for Portugal at Under-19s was also Bruno's first game for Portugal. Then we played together for the U21s, the national team and now we're both in Manchester so it's great. We're rivals but it's good to have him here.
"Changing is always complicated, you have to adapt to the way your new team plays, your team-mates, the way the manager wants to play, sometimes new systems. So maybe it will take him a few months but I think it's good that he's here and he'll be a great asset for Man Utd - but hopefully not against Man City."