Van Gaal's position has come under fire following United's Champions League elimination and their disappointing performances in the Premier League this season.
A 1-0 defeat to Midtjylland in the Europa League did little to help Van Gaal's cause, but Beckham continues to back the former Netherlands coach and has stressed it's not easy to be the man in charge at Old Trafford.
"Van Gaal is an experienced manager with a great reputation in the game. Sometimes it takes time. It is not easy being manager of Manchester United," Beckham told talkSPORT.
"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 has admitted he finds it hard to see United going through a difficult period, but he believes it was inevitable the club would struggle following the departure of manager Alex Ferguson and players such as Roy Keane, Paul Scholes and Ryan Giggs.
"As a United fan, I always hoped we wouldn't go through a slump, but it was inevitable. When the manager left that was always going to be a massive thing, but you also lost players like Keaney, like Scholesy, and Giggsy has stopped playing. You have lost such great characters through the team," he added.
"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.
"United is 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."