The pair also allegedly clashed a number of times behind the scenes, but the City game may have been a watershed moment in their relationship.
Mourinho, however, has told Pogba he wants to see greater consistency from him, particularly in training, with the United manager clearly implying the 25-year-old midfielder has not always hit the necessary standards.
"Mourinho backs you up if you give it your all and that's how I understand football", Herrera told El Mundo Deportivo. I instructed him to be fixed in a certain stage, ' acknowledged Mourinho.
'I told Paul after the City game I don't expect him to be man of the match every week.
"Do I expect him to score goals every match? No".
'That's the issue he has to position to himself, to take care of a certain stability, not have the good match, the so-so match and the damaging match.
'He really has to try to go for that stability and the first thing is stability at training level.
"But listen, he scored two goals so it's not down to me".
"We are a team that has beaten every other team in the Premier League - beaten every one of the top six".
Pep Guardiola's side have dominated the Premier League this season and will wrap up the title if United were to lose at home to West Brom on Sunday, or on Wednesday against Bournemouth. "We are not going to do anything insane", said Mourinho.
"We are not going to spend more than we can", he said.
Tierney signed a new long-term contract earlier in the season but the Mirror suggested last month that Celtic would consider cashing-in if £25m was put on the table this summer.
United came from behind to beat City 3-2 at the Etihad Stadium to deny their local rivals from being crowned champions, but Mourinho denied that the result was the best he had overseen since taking over at the club.
"But we are working really hard to try and finish second".
But with City's rise to dominance this season, a groundshare would add another dynamic to an already fierce rivalry which is arguably as relevant now as it ever has been.