The 67-year-old Dutchman also suggested United played more exciting football in his time at the helm than they do now.
The Red Devils had lost just one of his first 17 matches across all competitions under caretaker manager Ole Gunnar Solskjaer before suffering successive losses before the worldwide break.
United appointed him after he guided the Netherlands to an impressive 2014 World Cup, but despite spending 351 million euros on transfers, Van Gaal barely managed to win 52 percent of his games in charge.
"Beating Barcelona [in the Champions League] is a big ask because in the games against Paris Saint-Germain in the first leg and Juventus, I think they've shown a lesser level".
Although consecutive defeats to Arsenal in the Premier League and Wolves in the FA Cup have dented their campaign, United have got themselves back into the top-four race and are in the quarter-finals of the Champions League under their former striker.
Van Gaal's football was regularly labelled boring but in an interview with BBC Sport, he claims that both Solskjaer, just like Mourinho, deploys defensive tactics that aren't reflective of Ferguson's style.
"I am not there but there does look to be a change and the atmosphere seems to be better".
Ethiopian Airlines CEO: Boeing flight system may have triggered crash
As early as this week, Boeing is likely to start actual 737 MAX flight tests for the goal of certifying the new software. The update will also ensure MCAS is not triggered multiple times, as it was in the Lion Air crash .
The man himself announced his departure via Twitter, where he thanked the Manchester United manager he has worked under, other staff and all the players before stepping down.
But amongst all this, Van Gaal also talked about the team which could win the Champions League this season. I brought them back to 23.
Earlier, Legit.ng reported Manchester United have received a huge injury boost with eight squad members set to return from injury against Watford this weekend. "Then I had an open selection for the youth academy".
Solskjaer, like his mentor and former manager Ferguson, has given his talented and young attacking players - Rashford, Martial, Pogba, Lingard and co., the freedom to showcase their talents and push forward all the time.
Solskjaer at Old Trafford: five key things to know...... A chance is a game.
"You have to have British players in a title-winning team".
In his short stint as Manchester United manager, he has pushed principles that the club has always stood for - promoting youth players, playing attacking football, never giving up, and always pushing for success.