United now sit second in the Premier League table, five points behind their rivals Manchester City, and they will require consistent performances from all of their big players if they are to keep up with Pep Guardiola's side.
Mkhitaryan has not been the only creative or attacking player to come in for criticism from the United manager, with Juan Mata, Anthony Martial, Jesse Lingard and others left out at various times due to dips in form.
Mourinho revealed he has been unhappy with multiple performances that the Armenian has put in, and that form allowed him to give other players an opportunity.
"I was not happy with his last performances", said Mourinho of a player who has scored twice in 16 games this season.
And Mourinho believes that despite trailing only neighbours City in the Premier League goalscoring charts, his players are not scoring enough, with French worldwide Martial singled out as an example of a player who has responded well to being left out. "I'm not speaking about one or two, I'm speaking about three, four or five". He started well this season but his performance levels, goalscoring, assists, high pressing, bringing the team with him as number 10, were decreasing step by step.
The 28-year-old was a regular at the start of the season, but was dropped having been substituted in defeat against Chelsea earlier this month.
'I think it is quite fair that Mkhitaryan is back'.
"The team that excites more is the team that after five chances is winning 4-0". The Armenian had registered 11 goals and 15 assists in the 2015/16 Bundesliga season and was clearly a huge talent.
"So I can imagine, next week, you are going to ask - why is this player not playing?"
"For many weeks, the question was - why do they not play together?"
"All positions are open", he said.
Mourinho certainly will not shy from telling his players what to do, especially after slipping back into old habits as a lack of cutting edge saw them lose a match in Basel they dominated.
"The answer is very simple - until the worldwide board change the rules, I can only start with 11". "You have to perform".