The Netherlands boss, who is set to step down after the 2014 World Cup, would succeed at Old Trafford, according to his countryman
It is understood Van Gaal – who has also been courted by Tottenham – is keen to take over at Old Trafford in the wake of Moyes' sacking on Tuesday.
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Roy, who played under Van Gaal at Ajax, told the Daily Mirror: "He has definitely still got the hunger.
"I think he will die on the pitch, because he will never retire. He loves the job too much.
"He will never turn down Manchester United, believe me. I think it’s the job he really wants. And he will be a revelation at Manchester United."
Many players were believed to have grown distant during Moyes' tenure, but Roy believes Van Gaal's hands-on approach will suit United.
"He is, without question, the best manager I have ever played for. For me, he has proved himself to be one of the best managers and coaches in the world.
"He is very disciplined, very strict and is very attacking in his philosophy. I know English football well, and his style is suited to that.
"He believes in wingers, he is very strong and very tactical. The best word I can think of is demanding.
"On the pitch, every player will be told their job, they will know exactly what is expected of them, their position and role in the team. The way he prepares his teams is outstanding. In terms of organisation and tactics - the way he sets teams up will suit English football - is superb.
"I don’t know so much about fitness anymore and that’s the only thing he may lack, simply because you have to be so fit to play in England. That’s such a big part of the game in England.
"But if you look at the teams he has managed, they have always played attractive and exciting football. He will bring that to Manchester United. If he goes there, he will be a huge success."