The Red Devils thrashed LA Galaxy 7-0 in Van Gaal's first game in charge, with Mata - whose role under the new manager had been question prior to the Dutchman's arrival - featuring in midfield in a 3-5-2 formation.
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"The truth is we are trying to play with a new system,” he said. “I don't know how much time it takes - maybe one month or two but the most important thing is to believe in what we do.
"For me personally if I play behind the two strikers it's a good position. I can look for the ball. I feel comfortable in this role.
"This system can be very dangerous. But you have to communicate and co-ordinate."
However, despite his words of caution, Mata believes United must be challenging for the Premier League title this season, having finished seventh in a disappointing campaign under David Moyes' stewardship.
"This club was made to win," he said. "Ever since I was young Manchester United was winning trophies or fighting for them. That is what we have to do."
Mata also took time to praise Van Gaal's approach, revealing that he insists every player speaks in English on the field.
"We speak in English," Mata added. "The manager says we have to speak in English.
"He is very honest. He is straight as he speaks to everyone to their face. That is the perfect way to do it."