Roy Keane: Man United need five or six players but will bounce back
The Dutchman, currently in charge of his national team as they prepare for the World Cup finals in Brazil, is set to take over at Old Trafford on his return.
He will face the task of revitalising a club which slipped from being Barclays Premier League champions to the relative backwaters of seventh place after a bruising campaign under Sir Alex Ferguson's replacement, David Moyes.
However, Keane is confident the hugely experienced Van Gaal will turn United around.
Asked if the former Ajax and Barcelona manager is the right man for the job, he said: "You hope so.
"He is obviously a top manager, lots of experience. His contract was up with the national team, so that fell into place nicely.
"Fingers crossed, he'll be a manager. It's been a tough season for United - fingers crossed he'll do the business.
"I'm pretty sure he will."
Moyes lost his job last month after just 11 months in the position, with veteran midfielder Ryan Giggs taking over the reins for the final few weeks of a campaign which ended without a trophy or European football for next season.
Van Gaal will preside over a significant rebuilding programme as he attempts to restore the club's fortunes, and Keane is sure he will get the backing he needs.
He said: "Of course it's a big job. They need some players - I've said they need five or six players.
"They will bounce back. They are Man United."
With United seemingly ready to invest heavily this summer, they are already being linked with a series of potential targets.
McCarthy only joined the Toffees in a £13million from Wigan in September last year, and Keane, who has worked with him in his role as Martin O'Neill's number two since, suggested he may be happy where he is.
He said: "He's only been at Everton two minutes. He's obviously making good progress, but I'm pretty sure there will be lots of speculation about lots of players going to United.
"But James is at a good club in Everton, he has had a decent couple of seasons and if he keeps progressing, who knows?
"But I'm sure he's pretty happy where he is."