The Dutchman saw his first competitive game in charge of United end in disaster as the Red Devils suffered a shock 2-1 defeat at Old Trafford.
The loss has led to much criticism of Van Gaal, but the former Netherlands coach has received backing from former United manager Moyes, who was sacked after just 10 months in charge at Old Trafford following a disastrous Premier League campaign.
Speaking as a pundit for beIN sports, Moyes said: "Everybody knew it was going to take time. Taking over from Sir Alex Ferguson for anybody, it would take time.
"Louis van Gaal will need the time to do the job as well. He'll need to have that opportunity to change things and get a team he wants."
David Moyes has been out of work since being sacked by Manchester United
"What happened today happened to me against West Brom, Newcastle, and Everton last year," Moyes added.
"Every team in the Premier League is very organised now and quite often it's the special players that win you the games."
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