Van Gaal was handed the task of bringing the glory days back to Old Trafford following the failed reign of David Moyes, who replaced Ferguson when his successful 26-year tenure came to an end in May 2013.
Van Gaal spent over £150million on six new signings in the summer, but after 17 games United are third and trail Barclays Premier League leaders Chelsea by 10 points.
Luke Shaw, Marcos Rojo, Daley Blind, Ander Herrera, Angel di Maria and Radamel Falcao, along with several of their new team-mates, have all suffered injuries since moving to Old Trafford though, thus limiting their impact.
But once Van Gaal has a full compliment of players to choose from, the Dutchman will make United a real force to be reckoned with, according to Ferguson, who won 38 trophies during his reign at Old Trafford.
"I don't know how Louis van Gaal can expect to get the best results with the injuries he's had," Ferguson told BT Sport.
"When he gets the best players back, you watch United go - because he's a great coach, he will do well.
"They have still got great players.
"I'm not interested with what is happening with the players he's brought in, as that will take time.
"When I brought in Patrice Evra and Nemanja Vidic in the January of the same year, they were all over the place
They took five months to get used to playing for Manchester United - the culture and the history of the club.
"And these new players will be exactly same."
Michael Carrick also suffered a serious ankle injury in pre-season, but he is now fit again.
The 33-year-old has been key to United's recent upturn in form
Since he returned to the starting XI seven games ago, United have dropped just two points
Ferguson, who signed Carrick from Tottenham in 2006, lavished praise on the player.
"I think Michael's the best central midfielder in English football," he said.
"I think he's the best English player in the game."
Robin van Persie has recovered from a dip in form at the start of the campaign to score three goals in his last three matches.
Ferguson believes Van Persie, and fellow forward Wayne Rooney, will be key players in United's push for a top-four finish in the new year.
Ferguson added: "The World Cup has maybe taken a little bit out of Robin van Persie, but you watch him in the second half of the season
He will be fine.
"Rooney is back flying and he will always get you a goal
Having a goalscorer in your team is always an advantage."
Ferguson has also been highly impressed by the form of goalkeeper David de Gea, who has won United many points this term with a series of outstanding saves.
"The one that is most pleasing to me of the present lot is David de Gea," said Ferguson of the Spaniard, who made a number of costly errors after he signed for United in 2011 from Atletico Madrid.
"When we bought him as a kid he was really skinny but he had ability.
"He has special talents and he is showing that now and I'm really pleased for that kid."
Chelsea, and second-placed Manchester City, seem a cut above United this season.
Jose Mourinho's men have lost just once and only failed to win at Old Trafford in October because of Van Persie's late equaliser.
Mourinho was tipped as a potential successor to Ferguson, but the former Aberdeen boss selected Moyes instead - a move that backfired terribly and the former Everton boss was sacked after 10 months.
Ferguson still has a deep admiration for the Portuguese, especially because of the way he learned from the likes of Van Gaal and Sir Bobby Robson during the early stages of his career.
"It's unfair really because he's good looking
He has that George Clooney look about him with the white bits in his hair," Ferguson said with a chuckle.
"But he is a great example
He can speak five languages..
he goes and works with Bobby Robson, follows him to Barcelona, works there under Louis van Gaal.
"Then goes to a small team in Portugal (Uniao de Leiria), then to Porto, wins the league, wins the UEFA Cup, wins the European Cup, goes to Chelsea, wins the league twice in a row, then goes to Inter Milan..
that's an example to anyone who wants to do well - you shouldn't let the barriers be in your way if you want to get there.
"He never played the game, but he had the determination to be a coach."
Source : PA
Source: PA