Dutchman Van Gaal, who took over at United in July, spent around 150 million pounds (USD 238.8 million) to bring in six new players, including Argentine Angel di Maria for a British record fee.
The former Netherlands coach also let go a number of players who were signed or nurtured by Ferguson, causing critics to question the club's new policy of signing foreigners in favour of home-grown talent.
But Ferguson, who lead the club to 13 league titles during his glittering 26-year reign, backed Van Gaal's recruitment policy, which included signing Colombia striker Radamel Falcao on a season-long loan.
"It was really important because you need quality at Manchester United, you need the best players," Ferguson, speaking for the first time about Van Gaal's start at Old Trafford, said.
"When you can identify ability like that needed by Manchester United, they have the resources to do that. Those are fees I never quite equalled but nonetheless they were needing quite a big injection this year,” he added.
"Maybe he's doing the right thing to clear the decks and build his own team, because he's got the experience and coaching ability to do that. I think the way he's approached is brilliant," he further said.

The 72-year-old Scotsman also said he was encouraged that the Dutchman was giving youth players a chance with academy products Tyler Blackett, Jesse Lingard, Saidy Janko, Andreas Pereira, Reece James, Paddy McNair and Tom Thorpe all being handed their debuts.
"What has pleased me with Louis is he's given seven young kids their debuts this year and that falls into line with the history of our club," Ferguson explained.
"I think the supporters particularly respond very, very well when a young player gets his opportunity. Young people have to be given an opportunity, particularly if they've got ability. If you wait too long, they just stagnate and you lose them,” he added.
Ferguson retired in May 2013 and his successor David Moyes was sacked in April as United ended seventh in the table, their lowest finish in the Premier League since its inception in 1992.
Van Gaal, who has won league titles with Ajax, Barcelona and Bayern Munich, has endured a difficult start to his Old Trafford career.
His team suffered an opening day home defeat by Swansea City and twice squandered two-goal leads at promoted Leicester City to lose 5-3 either side of a humiliating 4-0 thrashing at third-tier MK Dons in the League Cup.
Ferguson, who won 38 trophies for United, pointed to his own difficult start when he was appointed manager in 1986.
"He's not been getting the results that are expected but when I came to the club I didn't get the results I expected myself at the beginning," he said.
"Louis is going through that same process and there's no doubt in my mind he will sort it out,” he added.
United are fourth in the league with 11 points and visit West Bromwich Albion on Monday.

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