After a tumultuous 2013-14 campaign under David Moyes, which saw the club finish seventh, Van Gaal spent £150 million during the transfer window in an attempt to get United back into the UEFA Champions League.
United broke the British transfer record to lure Angel Di Maria from Real Madrid in a deal worth over £59m, while Ander Herrera, Luke Shaw, Marco Rojo, Daley Blind and Radamel Falcao (loan) also arrived at Old Trafford.
And that spending spree received the tick of approval from United legend Ferguson - winner of 13 Premier League titles and two UEFA Champions League crowns in his 27-year stint at the club - who believes reinforcements were needed.
"That's the way the game is going today with fees like £85 million for Gareth Bale," Ferguson told MUTV.
"I think when you can identify ability like that needed by Manchester United, they have the resources to do that.
"They are fees I never quite equalled but nonetheless they were needing quite a big injection this year."
Ferguson added: "Herrera played against us three years ago for [Athletic] Bilbao in the Europa League.
"He's a talented young player and we scouted him quite a lot at that time. He's athletic, quite aggressive actually for a lad who has not got a great frame and he’s quite slim but he's quite aggressive and he gets around the pitch.
"The signing of Shaw was the one we tried to get when he was 16 years of age. They wouldn't sell him to us but they always said we'd be first to know if they ever did. He's a talented boy, a good footballer who likes to get forward all the time.
"I watched Rojo at the World Cup, I thought he did really well for them and I think he's capable of playing either left side as a wing-back if you like or as a centre-back.
"Daley Blind is one of those common-sense footballers that make up a team. He's probably a version of Darren Fletcher of a few years ago, that type of player. He's a good professional with common sense to his game. He keeps it simple and protects the defenders and the attacking midfield players in his role.
"The big one is Falcao who we're all waiting to see. Obviously, he has fantastic goalscoring ability. He had his injury so getting him on loan is the right thing to do."
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