Ordinarily the visit of the runners-up in the Belgian league would not cause much of a stir, but Van Gaal is under no illusions about the price of failure in the two-legged fixture, which concludes next Wednesday in Bruges.
Van Gaal worked tirelessly to turn United into a top-four team following their seventh-placed finish under David Moyes, but defeat would send the three-time European champions into the Europa League - and that is something neither the manager nor the board wants.
"Of course," Van Gaal said when asked if this was his most significant fixture as United boss.
"I have already explained, the players want to participate (in the Champions League) and the board wants to participate, but especially the fans want to participate so the pressure is high."
History suggests United should have an easy ride
The aggregate score of their last three home games against Belgian opponents is 18-1.
Brugge's squad has been decimated by injury in the build-up to the match, and they needed a stoppage-time winner to beat KV Kortrijk on Friday.
Van Gaal could have been draw against Lazio or Monaco in the play-off, but is still wary of the threat the Belgians will pose.
"I think it a difficult draw," he said.
"Brugge can defend very well and they can attack also, so it shall be a difficult match and that is why the pressure is high."
Brugge playmaker Victor Vazquez is hoping to deal a blow to his old coach on Tuesday.
Most of the players in the Brugge team will be unfamiliar to United fans, but Van Gaal knows all about Vazquez.
The Spaniard was coming through Barcelona's famous youth academy, La Masia, during Van Gaal's two spells as head coach of the Catalan giants.
Vazquez has brief but positive memories of the Dutchman, who highlighted the 28-year-old as one of Brugge's main threats at his pre-match press conference on Monday.
''It's always nice to hear about the big ones,'' said Vazquez when asked about Van Gaal's positive comments about him.
''I met him in Barcelona
I was young, maybe 11 or 12 years old but my impression was that he was a really hard coach with a lot of character and personality, just like he is now.
''I didn't meet him a lot of times but I think he is one of the biggest coaches in football, for sure.''
Brugge, who are managed by former Belgium goalkeeper Michel Preud'homme, are without eight players through injury.
United's only absentee is Phil Jones, who is out with mild thrombosis.
Van Gaal looks set to stick by captain Wayne Rooney despite his indifferent form in the club's opening two games.
''I have always confidence in my players," Van Gaal said when asked about Rooney, who has failed to register a shot on target so far this season.
''All the media has written for one year that I have to put him in the striker's position so it is very amazing that after two matches you already are doubting your own opinion
I cannot understand that."
Source : PA
Source: PA