The Dutch coach is expecting to leave Old Trafford in June 2017 when his current deal expires, although his future at the club remains the subject of intense speculation as United's season continues to disappoint.
Van Gaal has put his faith in a number of youngsters this season, most notably Cameron Borthwick-Jackson and Jesse Lingard as well as splashing out heavily on Anthony Martial.
The Dutch coach believes his successor will also need to give youth a chance and says the United board must be careful when making their decision.
"I hope people will look back in the future and talk of the young players as my legacy, but you can never tell," he told The Independent.
"The next manager would also have to show the confidence in the younger players. So I cannot judge.
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"If United, after I retire, hire a manager who does not give the benefit of the doubt to youngsters, it shall be very difficult.
"It is also very important for the board of Manchester United to look at the profile of the new manager.
"If they ask [for a recommendation on the next manager], I shall give my opinion and after that, they can do what they wish.
"But I never reign beyond my grave and, when I am gone, I cannot influence or contribute."