Sancho has struggled to find his best form since arriving at United and the Premier League in the summer.
The 21-year-old has two goals and zero assists in 23 games for the club, starting 14 of those matches.
"Difficult to say. I think it's a different league, it's a different competition," Rangnick said about Sancho in his most recent press conference.
"It's more physical, it's more pressure, although he also played for one of the biggest clubs in Germany, in Dortmund.
"But I think in total, the whole league, the whole competition is more physical and the level of expectation is higher. When he came to Borussia Dortmund as a young player, he was only 18. Now he's 21, playing for one of the biggest clubs in the world.
"I think it's also got to do with a lot of different things up here (points to his temple) in his head. But in training, whenever I see him train, he's showing that he's one of the best players in the training sessions. But now it's about the transfer to when he's playing and to showing to the same kind of level and performance on the pitch.
"It's a difference: if you come as an 18-year-old, unknown, talented English boy to Borussia Dortmund, from then on you can only improve, you can only make a success out of that.
"The level of expectation was a lot lower compared to the situation where you come at the age of 21, you come to a club like Manchester United for a high transfer fee, with a high level of expectation. Everyone expected from him that he would be one of the best players in the team. This is psychologically, emotionally a more challenging situation than the one at Borussia Dortmund and these are exactly the kind of steps that he has to make to become a top player for the next 10 years at this club.
"We can give guidelines, we can give him a helping hand and show him we are trying to accompany him on this way and give him all the necessary assistance that he needs but in the end it's up to him to take the next steps.
"For me, it is not at all a question of his position. His position is left or right winger, this is his best possible position. But again, it's not only about training at the highest possible level - I said that to him, by the way, the day before yesterday. Confirm the performances you show in training when you're playing on the pitch.
"It's clear in a 4-3-3 that he's a player for either of the wing positions, either left or right, he can play both. I think he would prefer a little bit the left side because then he can switch inside and shoot on goal with his strong right foot but, for me, there are no questions about his position. He's a winger, as we say in Germany someone who can dribble fast with the ball and, for me, there's not at all a question over the best possible position for him.
"With those kind of players, with creative offensive players it's all about confidence, being aware of how good they can be, then showing it in front of 75,000 or 45,000 at Villa Park. Of course, in the end he has to do that, he has to take that step again.
"In most training sessions, he is training at a very high level and now it's about letting that transfer onto the pitch in the league competitions, the Premier League, the FA Cup and the Champions League, but he can do that. He has the ability to do that, there is no doubt about that. But now we have to develop him into that kind of player, show him the same kind of performances that he has shown at Borussia Dortmund."
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