Di Maria, who joined United from Real Madrid this week for a British-record fee of £59.7million, was flanked by van Gaal at an Old Trafford press conference on Thursday.
The Argentina international's arrival has boosted a side that has taken just one point from the first six in the Premier League and suffered Capital One Cup embarrassment at the hands of third-tier side MK Dons.
But van Gaal struck a cautious note, insisting the club still faced a extensive rebuilding job.
"I'm very pleased that we have such a class player in our squad and it's important he is a team player - that's what I like about Di Maria," van Gaal told reporters.
"He can accelerate our play but he can also play in the interests of the team and that's why we've chosen him.
"I hope he shall give us good results but we can't expect, that after two days' training, he is the miracle I've read about."
Tuesday's 4-0 defeat in Milton Keynes brought van Gaal's tactics - notably his favoured 3-5-2 formation - under further scrutiny and while he remains committed to instilling a fresh approach, the Dutchman admitted his latest capture offers flexibility.
"He fits into our philosophy so I can change the system for him and maybe I shall do that in the future, like I have already done against Swansea City," van Gaal added.
"He played at Real Madrid not only as a wide wing player but also in midfield so that is also a reason why we are convinced he shall succeed."
Di Maria, who should go straight into the squad for Saturday's trip to Burnley, declared himself happy to play wherever required.
"It depends on the manager and where he wants to play me," United's new No 7, speaking through an interpreter, said.
"I come here to work for the team and I am prepared to play in any position he wants to. I just want to help the club become successful again."
Van Gaal expects to do further business before Monday's deadline but would not go into details.
He said: "I cannot say anything about that because it will raise the price. The club shall come, like now with Di Maria, when the time is right to announce it. We cannot react to every rumour.
"Also, players shall go in the meantime. I had a conversation with the players after lunch and I said, after this weekend, we shall maybe have another group. Players will go away and others will come in. We have to wait and see."