The highly-coveted Argentina international joined United this week in a record £59.7 million deal from Real Madrid.
The 26-year-old has been handed the club's famous number seven shirt and his arrival has the potential to excite fans after a poor start to the season.
Van Gaal, however, has warned he cannot be expected to transform fortunes immediately.
Van Gaal, speaking at a press conference to unveil Di Maria, said: "I am very pleased that we can have such a class player in our squad but you have many class players.
"For me it is also important that he is a team player and that is what I am liking in Di Maria - not only class, and that he can accelerate the game for us, but that he can also play in the interests of the team.
"That is why we have chosen this player and I hope he shall give us good results, but we cannot expect after two days' training sessions that he is the miracle what I already read (about).
"No, you have to work for the miracle and he knows that."
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- Van Gaal