He admits it will be a odd experience to line up at his old stomping ground in the colours of a different team, but says he will not allow sentiment to cloud his focus.
Mourinho, who has been staying at the Lowry Hotel since taking over from Louis van Gaal, only recently returned to the UK following United's Super Cup defeat by Real Madrid earlier this week. He is a key player in midfield.
Mourinho said, as quoted by the Manchester Evening News: "You know he's injured, he needs time to recover, he's not ready to play tomorrow". If you are a Manchester United player you've got to have personality, you've got to have that aura about you.
Having led United to League Cup and Europa League glory last season, Mourinho's challenge for the new campaign is to turn them into title contenders.
In search of goals, United turned to last season's second-highest scorer.
"We saw how hard it was for him to get used to losing, it was an unknown territory for him, not easy to deal with, he dealt with it in a certain way, so I go with Man City".
Herrera says United simply came up short against the "best team in the world" - a philosophical stance that echoed his manager's post-match thoughts.
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PSG wanted Neymar to start the season at the Parc des Princes but his debut was delayed because of the paperwork issues. When you like competition, you like to play against the best. "It's in this spirit that you do your job".
Hernandez is now likely to make his Premier League debut for the Hammers against his former club and said of the Red Devils ahead of the game, "It was a great experience [there] ... only happiness".
"Some of the transfer fees are insane but it shows how good these players are".
"We are in a position to do quality work better than we did in the first season, so I am convinced that our second season, in terms of the quality of our team, is going to be better".
The Swede has since been released but Mourinho splashed £75 million on Romelu Lukaku, who scored 25 Premier League goals for Everton last season.
Manchester United kick off the new Premier League season when they entertain West Ham at Old Trafford on Sunday afternoon. They have to play on the Thursdays, but the top seven are going to be in the four competitions, so no advantage for any one of us'. We also got a central midfielder and a striker.
United trailed home in sixth place last season, 24 points below champions Chelsea, and have finished in the top four just once since Alex Ferguson retired as manager in 2013. Given the current markets City are not value but we do not want to oppose them... our only BACK (long position) pre-season is Chelsea.
"At my other clubs, what I had was more players scoring goals".