Van Gaal will quit his post as the Netherlands' head coach after this year's World Cup and has agreed to take over at Old Trafford, following the sacking of David Moyes earlier in April.
|MAN UNITED LATEST
|16/1||Man Utd are 16/1 with bet365 to beat Sunderland 4-0 on Saturday|
"I will say more about Louis and United once his appointment is official," the former goalkeeper is quoted as saying by the Daily Mirror.
"But I have made it clear here before that Louis van Gaal is the best manager I have ever played for.''
Franz Beckenbauer was president of Bayern Munich when the Bavarian club lured Van Gaal to Germany and believes the veteran coach would be "perfect" for United.
"He would be perfect for Manchester United because he is an internationally experienced coach and he understands English football," Beckenbauer reportedly told the Daily Mail.
"I don't know if it's a rumour or if they're really trying to sign [Van Gaal] but if they agree with Louis I think it would be a good part of the future.
"He won a lot of titles so he is experienced and he is ambitious. He has the personality. He has everything."
Van Gaal won the Bundesliga-DFB Pokal double with Bayern in the 2009-10 season but was sacked in April of the next campaign as the German giants slumped to third.
But Beckenbauer remains convinced the Dutchman is "one of the best coaches in the world", despite Van Gaal's reputation for arrogance.
"If you ask him a stupid question then it can be that his answer is a bit arrogant but if you treat him with respect, then respect comes back to you," the 68-year-old said.
"I like him. He was also very successful with Bayern Munich. In the end there was a little discussion about the way he was handling his job so that's why they went separate ways. But for me he's one of the best coaches in the world."