Both missed England's two matches during the international break and the Dutchman wants them back as United attempt to put a demoralising 3-0 defeat against Arsenal behind them.
"We cannot accept it. We've spoken about this. It cannot happen again," he said.
"We want to be the champions, so we must behave like champions. You have to improve every time.
"It is not only the players it is the staff, all the members of the staff.
"Everton is also a difficult opponent. Of course I'm confident, because I have seen the training sessions and the reaction of my players.
"But you cannot be sure it will be the result that you want."
Van Gaal said that because the international break came immediately after a defeat, with so many players away, it had been "an awful two weeks".
United had been top of the table after three successive wins but dropped to third after losing to Arsenal, two points behind leaders Manchester City.
(Reporting by Steve Tongue; editing by Toby Davis)
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