After admitting on Monday that the United squad that he inherited was "broken", the former Netherlands boss has gone a step further in suggesting that it could take a while to fix the problems inherent in the club and get the squad to adapt to his style.
Van Gaal told reporters on the club's pre-season tour of the United States in Washington, DC: "Every club where I have been, I've struggled for the first three months.
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"The way I train and coach is in the brains, not the legs, but the most important thing is they have to know why we do things. When they do, the footballer is not playing intuitively.
"A lot of players are playing intuitively and I want them to think and know why they do something. That process is difficult at first and in the first three months. It takes time."
Van Gaal also cited his time spent at Bayern Munich between 2009 and 2011 as an example of a slow start under his management before eventual success.
"When we survive the first three months, it will be the same as for me as it was at Bayern Munich," he added. "At Bayern, after the first three months, we were sixth or seventh and we were third in our Champions League group.
"We had to win at Juventus and did – that was the turning point. Now United have me, a new manager, so new chances for the players but we have to create a way of playing that isn't the same as before and that's difficult for them.
"They have to perform under pressure and have a to decide [what to do with the ball] within one second and that is not easy."