The Dutchman was in line to take charge of the Belgium national team just months after leaving United in 2016 and before Roberto Martinez was appointed.

Van Gaal was sacked two years into his three-year deal and would have had to give up a portion of his pay-off to take another job.

"It would have been really great if I had become Belgium national coach, but I was so resentful and vindictive that I let that job go by," Van Gaal told De Volkskrant. "It was stupid, really, because the sporting value should always come in the first place. That should have been the most important thing. But that's how I looked at things. It was not about money. It was all about the act of revenge.

"I went for my instinct, not the rational. I just have to live with that. I've been a really successful manager, so I don't want to slag the world of football down. I have had a lot of good times.''

United appointed Jose Mourinho just weeks after Van Gaal was dismissed.

It followed months of speculation the Portuguese coach could take the reins and Van Gaal, 66, did not like the way he was treated by the club.

"The way Manchester United have treated me was terrible," he said. They have been mean and low. In contrast, the way president [Joesp Lluis] Nunez of Barcelona treated me was fantastic. That proves that the world of football is not full of false people. There are also straight and warm people among those people."

Van Gaal was sacked after winning the FA Cup in his final game in charge, but fourth- and fifth-place finishes in the Premier League sealed his fate.

There were also questions about his style of play, and Van Gaal has accused former United players of a campaign of criticism that he says eventually reached the dressing room.

Paul Scholes was one ex-United star to voice his unhappiness, at one point describing the the Dutchman's football as "shambolic."

"The former players of United started to have a go, saying that I was giving the fans boring football," Van Gaal said. "That struck me. It was directed, organised. After a while, I started to think I'm losing my authority this way towards the players. So I had to make concessions in my approach of the players.

"That was tough, because I've always had my own way of coaching."