After an unbeaten pre-season, which included five wins on their tour of the United States, Van Gaal's team opened their Premier League campaign with a disappointing 2-1 defeat to Swansea City at Old Trafford last week.
Questions marks have since been raised as to whether United will miss out on European football for a second consecutive season, having finished seventh in 2013-14.
But speaking ahead of Sunday's trip to Sunderland, Van Gaal urged the Old Trafford faithful to believe in the new philosophy, as he looks to bring success back to the club.
"I think the fans of Manchester are intelligent and I have already said in all the press conferences in the United States that the first three months shall be difficult for the players especially," Van Gaal told reporters on Friday.
"But also for the fans and I said also to Ed Woodward and the Glazer family and it is like that.
"They have hired me because of my philosophy, not because I am a very nice person, I am but it is my philosophy they have hired and I am not hired to be fired."
The Dutchman added: "I can imagine that fans are also scared because they have seen already the last year and now also the first home match and I can imagine that.
"They have to believe in the philosophy that we bring in this club and the players are believing and they have showed it in the United States.
"Now they have to show it here and that needs time."
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