The forward came back to the club after being at the Copa America and being linked with a move away.
When a move to West Ham United or Chelsea did not work out, Duran got his head down and has started performing for the Villains.
"He’s certainly got his focus back," McGinn said of Duran after a win over Leicester, in which Duran scored.
"For a young player to have so much attention and speculation surrounding him … he’s a character, you can see that at the training ground.
"I was quite hard on him last season after one of the games in an interview. Just about his attitude and how he can improve that, but in all fairness I’ve been pleasantly surprised.
"I think the coaching staff and players have been pleasantly surprised too about how he has handled it all. He’s an Aston Villa player. He’s trained really well. He has all the attributes to be a world-class striker and we’re seeing glimpses of it now.
"It’s credit to him for being focused. If you come and watch training now, he’s focused and he’s sharp and ready to go. Hopefully, we can see more of that and it’s up to us, as players, to make sure he keeps going in the same vein."
McGinn added: "He doesn’t seem to have let anything in the summer affect him. Maybe the penny has dropped for him. He’ll get his opportunities, chances and his goals and even his attitude off the pitch.
"The way he is around people, around the staff - it has improved a lot - and it’s great to see. We don’t want to see him lose his character, his sense of fun - we don’t want him to lose that - but it’s about doing it at the right times and hopefully he’s found that."