United are still on the hunt for a new manager after sacking David Moyes almost two weeks ago, and Holland boss van Gaal is currently the clear favourite to take the job after the World Cup in Brazil finishes this summer.
Many have recommended van Gaal for the job so far, andRoy, who featured over three seasons at the City Ground, played under van Gaal at Ajax at the beginning of his career, and has now joined the movement in pushing for the 62-year-old to be the man in the hotseat at Old Trafford.
"If there is one manager who can do the Manchester United job - he can. He knows how to create young players and win games against big teams. With his tactical mind and the way he thinks about football, the Premier League is going to have a very difficult time playing against Man United next season," said Roy.
"It's going to be his biggest job. As a team coach, the Man United job is the biggest to be had and you can be sure he is preparing himself very well. He's with the national team for the World Cup and I hope he does well with them first."
There are some concerns over the coaching staff that van Gaal would be working with at Old Trafford, with some suggesting that the deal to take him to United had hit a snag over the Dutchman wanting to bring in his own staff, and Roy also confirmed that van Gaal would want to hire his own men to assist him.
"Louis will definitely bring his own team in but it's Manchester United so you also need to be able to work with people already in the club. I think he might keep Ryan Giggs or Paul Scholes, or maybe both of them," concluded Roy.