#3 Continous moaning about the transfer market
Manchester United finished second in the Premier League last season as the manager looked to strengthen the defence to fight for the league title his campaign. It's believed that Mourinho shortlisted few central defenders in the summer, most notably Toby Alderweireld of Tottenham Hotspur and Harry Maguire of Leicester City.
However, the board decided not to back the manager with any more funds as the players bought in previously didn't do much to improve the squad. In his two and half seasons at the club, Jose Mourinho had already spent more than 300 million on transfers without any significant outcome.
The unsuccessful transfer market irritated the Portuguese who didn't leave any stone unturned to take a dig at his side's weak defence. Mourinho's negative attitude towards his players has reflected in the team's performance as well with the players committing far too many defensive mistakes than it was hoped for.
The broken relationship with the board made his exit more imminent.