Jose Mourinho says he needs time to change the mentality of the players who were coached by his predecessor Louis van Gaal.
Mourinho took over as United boss in May as successor to the sacked Van Gaal, who was criticised by supporters for his style of play at Old Trafford.
Mourinho was keen to stress his own philosophy was simply "different" to Van Gaal's rather than better - and he admits that fans will have to be patient before they see the work he is doing with the squad.
He said: "My teams are different to Mr Van Gaal's teams.
"I want to make it clear that I am not saying my teams are better or have better ideas or my principles of play are better. Not at all.
"My teams are different to Mr Van Gaal, and it is a difficult situation to change the dynamics. It would be easier for me to have 20 new players and start from zero. For two years, they had some principles of play that are not mine - clearly, they are not.
"But the players are players and, without losing their identity, they always try to adapt to what the manager wants.
"Of course, after two years of work, there are things in their brain that are automatic, and that is difficult to change. But we are working hard and the players are trying everything.
"Of course, we make mistakes and we are far from perfection, but they are giving everything to adapt, and step by step my team is going to be my team."
Sunday's Community Shield game with Leicester at Wembley is their last before the Premier League begins.
Asked if he saw it as a trophy opportunity or a fitness exercise, he said: "Everything is important.
"Our pre-season was strange - good for some players but not enough for others. The number of matches was not enough.
"We need to train against other teams like we did against Everton and Galatasaray, but that is over. Now we have no chance to train against other teams. Now we have Leicester before the Premier League and it is not a training session against another team - it is a game.
"We have six changes [substitutions], not three, so that gives me the chance to give minutes to some people, a chance to play with some players who I know cannot have the condition to play for 90 minutes.
"So it will be a little bit of everything - and, of course, we will try to win it."