After struggling under David Moyes last season, Van Gaal and chief executive Ed Woodward entered the transfer market to bring in Angel di Maria, Radamel Falcao, Luke Shaw, Marcos Rojo, Daley Blind and Ander Herrera.
Despite backing the business completed by the Dutchman, Ferguson has also applauded his decision to use a number of academy graduates in the early stages of the new campaign.
"When you can identify ability like that for Manchester United, they have the resources to do that - fees I never quite equalled but they needed a big injection this year," Ferguson, who won 38 trophies with the club, told MUTV.
"The rebuilding of the team, they've brought in some good quality which is really important because you need quality at Manchester United, you need the best players.
"What's pleased me about Louis is he's given about seven of the young kids their debuts, which falls into line with the history of the club. I think the supporters will respond well when a young player gets his opportunity."
Van Gaal's side currently sit fourth in the Premier League table.