Jose Mourinho’s style of management is simply too demanding for some players, according to the Portuguese manager’s biographer Manuel Pereira.
The Red Devils were struggling to score goals and had their top four hopes slipping away when the decision was made, with Ole Gunnar Solskjaer stepping into the interim manager role.
United have not lost since, having come away with six straight victories, including a 1-0 triumph over Tottenham at Wembley on Sunday.
The reason for the struggles this season under Mourinho remain a mystery to both the manager and his biographer, though Pereira admitted it was clear the dressing room had been lost by the end.
“I'm sure not even Mourinho himself has a clear answer to [what went wrong],” Pereira told Goal. “There were difficulties between him and the responsible persons from the beginning.
“He wanted players he never got. This frustrated him because he did not think he could play for all titles with this team.
“At the beginning, however, he got along with the players. This was also shown by the success in the Europa League.
“By the beginning of this season, however, he lost more and more of the support of the locker room until he was no longer acceptable. You see how big his problems with the team were at the end, when you look at how the team plays now under his successor.”
Given what happened at Mourinho's prior stops, most notably at Chelsea and Real Madrid, that was not a surprise to Pereira, who notes that many players cannot handle Mourinho's management style for more than few years before things begin to fracture.
“Mourinho is a trainer for shorter periods,” Pereira said. “He's never been in a club for more than two or three years, has success first, and finally gets into a fight because the chemistry inside is not right.
“That's just Mourinho. A very ambitious and demanding coach, but for some players after a certain time, too demanding. They will eventually relax and rest.
“That was also the case in Manchester - and foreseeable for me before the season.”
Pereira attributed part of the problems to Rui Faria’s departure from the club, though he did note Mourinho’s frustration with the club’s transfers also played a role
“[Rui Faria] was something like Mourinho's right hand, Mourinho's mirror – a footballer who understood Mourinho's way of working better than anyone else,” Pereira said. “The separation from him, but also the failed once again transfers were ultimately crucial for Mourinho's failure.”
And Pereira was not surprised United ultimately decided to part ways with the manager, given the circumstances. With the squad dissatisfied, it was a choice between them and the manager with only one outcome possible.
“It's still cheaper to fire a coach than a whole team,” Pereira said. “Those responsible no longer had a choice. The pressure was huge. A club like Manchester United can not settle for sixth or seventh place.
“Even if teams like Liverpool or City are stronger: A Champions League course should be able to be reached with this squad.
“Although Mourinho did not get every player he wanted, a lot of money was spent without a reasonable return.”