Pep Guardiola's City travel to Old Trafford on Sunday looking to extend their eight-point advantage over second-place United at the top of the Premier League table.
It is being billed as an opportunity for United to blast their way back into the title race and Mourinho lit the blue touch paper in his pre-match press briefing by suggesting City's players went to ground too easily.
"They are a good team. They defend well, they react well to the moment they lose the ball," Mourinho told reporters at United's training base in Carrington, west of Manchester on Friday.
"They have a good dynamic in attack, they have creative movement. They have amazing players, they have a fantastic coach, they have lots of good things. If you ask me one thing that I don't like a lot it's that they lose their balance very easily. You know, a little bit of wind and they fall."
Arsenal manager Arsene Wenger accused City winger Raheem Sterling of diving last month, while midfielder Fernandinho was booked for simulation during his side's recent win at Huddersfield Town. Mourinho also questioned Guardiola's right to wear a yellow ribbon in solidarity with imprisoned Catalan politicians, suggesting he would find himself in hot water with the authorities if he made a similar gesture.
"I think I wouldn't be allowed to do. That's just what I think," said Mourinho, who famously clashed with Guardiola while the pair were coaches of Real Madrid and Barcelona respectively.
"If the rules allow us to do that, he is a free citizen to do it. But I am not sure if the rules allow to have any political message on the pitch. That's just my doubt. But I know Pep and I know his feelings like everybody else knows because it is public about his country."
Mourinho also moved to draw a line under his recent feud with United's fans.
He criticised United's fans for voicing dissatisfaction with Romelu Lukaku during October's 1-0 win over Tottenham Hotspur at Old Trafford, which saw the Belgian striker fail to score for a fifth successive match.
Mourinho also hit out at supporters for booing when he took Anthony Martial off in the same match and used his programme notes prior to a Champions League game against Basel to criticise the atmosphere during the Spurs game.
United fans expressed disappointment with Mourinho's comments on social media and on Friday he decided to call a truce. "I stop with that," said the Portuguese, who will be without the suspended Paul Pogba against City.
"I'm not going to write any more words about it, I'm not going to say any more words about it. We are paid to work and to work hard and to give the best we can, not to criticise fans and I'm not going to say any words. It is the reality of things. I'm not paid to come here and make any comments or to ask for something from the fans. I am paid to give them happiness, which is what I try to do every day."