The Portuguese initially delivered on his remit upon taking the Red Devils’ reins, with three trophies secured in his debut campaign.
He then led his side to a runners-up finish in the Premier League, before history repeated itself and he failed to see out a third full season in a prominent coaching role.
Mourinho was relieved of his duties in December 2018, with United forced into taking action after seeing their season implode against a backdrop of reported rifts in the camp.
Former Red Devils defender Parker believes such an ending was always on the cards, with a coach who remains a proven winner having refused to alter his approach or take important lessons from illustrious mentors that helped to put him on a path to the top.
“He’s probably never going to be a ‘nice guy’ like Ole Gunnar Solskjaer is, but some people in football are too scared to talk about him for fear of the consequences,” Parker told Eurosport.
“Mourinho never smiled, which doesn’t make any sense. He should have been happy – he was in a job that he’d always wanted, one of the most prestigious jobs in the world at one of the biggest clubs. He was acting like he was at Carlisle United, not Manchester United.
“Things might have tailed off for United under Solskjaer, but Mourinho doesn’t get it. When you come in as an interim manager, your job is to fill a role. You have to pacify players and you don’t do that by going in and shouting at everyone. You calm things down at the club and then start to earn the respect of the players.
“To be fair, Mourinho might have a point about some of the players, but it doesn’t mean he was right to carry on as he did. They might have been difficult to work with. Some of them were stale, some of them were bad apples, and some of them weren’t good enough to challenge at the top, but Solskjaer didn’t ruin the atmosphere at the club, instead he gave them hope.
“Look at the game against Paris Saint-Germain, they could never have done that under Mourinho. You have to work with what you’ve got, whether you think there should be improvements or not.
“He was the one to blow his golden opportunity – it’s not anybody else’s fault.
“He didn’t buy well, and he bought Alexis Sanchez, which was a disaster for the club’s finances and the team. He was fitting a square peg into a round hole, and it was totally unnecessary. Nobody made him do that.
“The problem with Mourinho was that he wanted to be a manager, which misses out at least half of the responsibility of the job, which was to be a coach.
“He’d worked under one of the great man managers, Bobby Robson, but it seemed he learned nothing from him. When Bobby saw weakness, he managed it and mitigated it, he didn’t scream and shout.
“The very best managers plan for a year ahead, they don’t burn all their bridges in anticipation of problems.”
Mourinho has remained out of work since leaving United, but has expressed a desire to return to the dugout this summer and continues to be linked with various posts across Europe.