United, winless in their last five games in all competitions and beaten in their last two, are out of the UEFA Champions League and fourth in the Premier League, six points behind leaders Leicester City.
Their playing style under Van Gaal has been widely criticised and reports have suggested there has been player unrest in the camp.
The Dutchman has dismissed such talk, stressing his belief the squad are behind him, as well as the club's hierarchy.
But, as he acknowledged in the wake of Jose Mourinho's sacking at Chelsea that no manager's job is safe, Van Gaal also made it clear he knows his own position could come under threat should United not start doing what he has emphasised they must - quickly start putting more points on the board.
Asked on Friday ahead of Sunday morning's (AEDT) home league clash with Norwich City about the relationship between him and his players, Van Gaal said: "It's fine.
"I've said that already more than once, but I have seen articles that it's not like that. It is a little bit crazy.
"I have the full confidence of my board and my players I feel.
"But we have to get results. We have to win, and we know that. There is not any doubt.
"We have to win because when you lose too much, also for me it's the end of the world."
Van Gaal had already by that point emphasised the importance of player-manager 'chemistry' as he expressed his shock at the news about Mourinho.
Van Gaal said: "It was a big surprise to me.
"He is a fantastic manager with a record that nobody has in this football world, but it is still possible.
"The main thing is always, of course, first the results, and second, the chemistry between the players and the manager and staff."
When asked if the fact Mourinho had been axed so soon after guiding Chelsea to the 2014-2015 Premier League title showed no manager was safe, Van Gaal said: "Yes, it is like that. But we know that in advance. Also Jose knows that. This is the world."
United have drawn four of their last six home games 0-0 and among the critics of a playing style widely regarded as dull are some of the club's fans, who have been voicing their frustration at matches with boos and shouts of 'attack, attack, attack'.
Asked about that disgruntlement and whether he felt the supporters were still with him, Van Gaal said: "It's always like that when you lose. Then fans have to prove their belief again.
"The board can see what you can do as a manager in practice but the fans cannot see that, so when you lose you need the belief of the fans.
"It is a question for the fans, not the manager."
United could have skipper Wayne Rooney (ankle) - whose next appearance will be his 500th for United - along with Chris Smalling (groin) and Ander Herrera (hamstring) back in action against Norwich, with all three having trained for a full week building up to the match.
Van Gaal said of Rooney, out for the last three games: "It is possible he can play, but we have to wait and see. I hope when he plays he scores a goal, because it is a big day for him.''
Ashley Young (knock) is a doubt, while Jesse Lingard (leg) and Matteo Darmian (hamstring) are unavailable.
Meanwhile, Van Gaal has given a non-committal response to questions about the possibility of recalling striker James Wilson, who is on loan at Brighton & Hove Albion until the end of the season and has so far scored twice in four games for the Championship side.
"We believe in him," Van Gaal said.
"He is showing his qualities, but at a lower level.
"When we are in trouble, we can recall him. It's a matter of a decision at a time that maybe comes, but maybe not."