The United legend says critics of the Dutchman should listen to the views of those who know him best.
United coasted into the quarter-finals of the FA Cup with a 3-0 win at Sky Bet League One side Shrewsbury on Monday night.
The Red Devils, though, face a battle to continue their Europa League campaign, needing to overturn a 2-1 first-leg loss when they tackle FC Midtjylland at Old Trafford on Thursday night.
After that comes Sunday's visit of Barclays Premier League title challengers Arsenal.
It is a lack of consistency this season - United are only in fifth place following seven league defeats - which has seen pressure increase on 64-year-old Van Gaal
Former Chelsea manager Jose Mourinho is reportedly being considered as a successor.
Beckham, who was an integral part of Sir Alex Ferguson's all-conquering squad, sees no reason to wield the axe at United, even though he would love to see Mourinho back involved in the English game
Beckham told TalkSPORT: "He (Van Gaal) is an experienced manager with a great reputation in the game. Sometimes it takes time. It is not easy being manager of Man United.
"We have to look at results, we have to look at the way we play, we have to listen to fans - the people that really matter at the club - and I only hear great things about him as a person, as a manager, as a coach.
"I have met him once before and he treated me unbelievably well.
"He is manager of Manchester United so there is always going to be criticism, but at the end of the season let's see what happens."
Beckham left Old Trafford for Real Madrid in 2003, before spells with Los Angeles Galaxy, AC Milan and Paris St Germain ahead of retiring in 2013.
He sees no reason why Mourinho should not make an impact again in the Premier League, wherever he works next.
"Jose leaving Chelsea, who would have expected that after the season they had last year? It doesn't make him a bad manager," said Beckham.
"He is still one of the best managers and I hope he comes back to the Premier League as soon as possible.
"The Premier League is the Premier League for the great players we bring in, the great teams, the money, the fans and the great characters that we have as managers. You want to see managers like that in the game."
Beckham, 40, believes it was always going to be a tough act to follow Ferguson, under whom the midfielder won six Premier League titles as well as the 1999 Champions League in their treble season
David Moyes lasted under a year, and Van Gaal has also found the job a tough challenge.
"As a Man United fan, I always hoped we wouldn't go through a slump, but it was inevitable," Beckham said.
"When the manager (Ferguson) left that was always going to be a massive thing, but you also lost players like Keaney (Roy Keane), like Scholesy (Paul Scholes) - and Giggsy (Ryan Giggs) has stopped playing.
"You have lost such great characters through the team, and (former chief executive) David Gill stepped away from Manchester United. They are all integral parts of the club.
"We have had so much success over the last 20 years that if we don't win something for one season or two seasons people talk about it being a crisis.
"Man United is Man United. It doesn't matter if you love them or hate them, they are one of the biggest, if not the biggest, club in the world and you have to keep that reputation. The only way you can keep that reputation is by winning trophies."
Source: PA