Dutchman van Gaal was drafted into Old Trafford in a bid to halt last term's alarming slide, when the 2012-13 champions finished in seventh place after a series of insipid performances under David Moyes, who lasted 10 months as Alex Ferguson's replacement.
After leading the Netherlands to third spot at the World Cup, the Dutchman raised hopes that the force of his personality could lift the club out of the doldrums as United enjoyed an unbeaten pre-season that included wins over European champions Real Madrid and Liverpool.
However, Saturday's 2-1 opening day loss to Swansea, and the once unthinkable sight of fans leaving Old Trafford early after another ponderous attacking effort, highlighted that it will take more than a change at the top to breathe new life into the club.
Before kickoff former Liverpool forward and BT Sport pundit Steve McManaman branded them the worst United side he'd seen in 20 years, while Alan Shearer said on Match of the Day: "They need at least three world-class players".
Van Gaal said the need for new players had already been identified, while chief executive Ed Woodward has insisted they have the funds available to splash out.
Indeed, close to 60 million pounds ($100.39 million) was spent on midfielder Ander Herrera and defender Luke Shaw in the past few months, while they broke their club transfer record bringing in Juan Mata from Chelsea in January.
ABILITY TO COMPETE
However, with Luis Suarez joining Barcelona from Liverpool for 81 million euros ($108.47 million) and Colombia World Cup star James Rodriguez moving to Madrid from Monaco for a similar amount, questions continue to be asked about United's ability to truly compete.
The Glazer family which owns the club remain deeply unpopular with those who accuse them of burdening United with debt which hampers their spending ability, while whether the big names even consider them an attracting proposition anymore remains in question.
Madrid paid less for German World Cup-winning midfielder Toni Kroos than United did for Shaw, highly promising but a teenager untested at the highest level.
Regardless, the way defensive errors helped Ki Sung-yueng and Gylfi Sigurdsson find their way past David de Gea in United's goal, condemning the hosts to their first top flight opening day loss at home since 1972, remains the more immediate concern.
Injuries forced van Gaal to field Tyler Blackett and Jesse Lingard in defence, while Chris Smalling and Phil Jones were less than convincing.
New captain Wayne Rooney, who levelled the scores from close range just after halftime before Sigurdsson's late winner, said they were not interested in what other people were saying as they looked to improve on last season.
"We are not out to prove people wrong," he said. "We are out to win things for ourselves, the fans and this club."
"We know last season was a disaster. It wasn't good enough. And it's always a bigger story when Manchester United struggle - you are going to get ex-players having their say. We have to accept it and be ready for it.
"We know that if this club is successful it is great and if it is not then there are a lot of people who are waiting for you to fall so they can get at you. We have to make sure we are successful. We have to make sure last season was a one-off because that was not good enough."
($1 = 0.5977 British Pounds)
($1 = 0.7468 Euros)