The Portuguese was sacked in December, leaving the club in sixth place in the league and 11 points outside of the top four.
Mourinho spent £360m in two-and-a-half-years at Old Trafford but rivals Liverpool and Manchester City surpassed his spending last summer.
United agreed a non-disclosure agreement with Mourinho when he was sacked to prohibit him from discussing his time at the club but the 55-year-old threatened that agreement with a sly dig at the club’s board during his punditry role with beIN Sports.
‘For me it is more complicated as a manager as I don’t focus on the football itself, I have to focus also in what is to prepare the future,’ said Mourinho.
‘I think the future starts to be prepared with principles. That is more important than the football you watch and comment on. It is more important the culture you bring to the club, the principles, so it is a bit more complex.
‘But you have the case of Manchester City. In the first season, Guardiola was not a champion, it was really difficult and people were expecting a winning Manchester City.
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‘Some of the players were already champions twice, Sergio Agüero and Vincent Kompany, and in the first to the second season Pep made great decisions, but great decisions that were supported.
‘For example, he didn’t want Pablo Zabaleta or Bacary Sagna, two right-backs, and he didn’t want Aleksandar Kolarov or Gaël Clichy. In the same summer he sold four full-backs and got four full-backs. He got Kyle Walker, Danilo, Benjamin Mendy and another. He was supported.
‘I think how many players were in Liverpool before Jürgen arrived. No Alisson, no Virgil van Dijk, no Andrew Robertson, no Mohamed Salah, no Roberto Firmino, no Sadio Mané, no Fabinho, no Georginio Wijnaldum, no Naby Keïta, so this is work in depth.
‘If you are manager and you have in your hands the possibility to choose the players you want to follow your football idea, or to follow the idea that you think is the best to win a certain competition, that is one thing. Another thing is if you are not able to do this.’
Mourinho confirmed on the show that he has rejected three job offers since leaving Old Trafford.
Former club Benfica were said to be keen on appointing Mourinho but the Portuguese is believed to be targeting a return to former club Real Madrid.
United have won seven on the bounce since Mourinho’s departure with Ole Gunnar Solskjaer transforming the club’s style of play.