Madrid will host the Premier League champions on the back of only one victory in four league games, leaving it eight points behind leader Barcelona.
Cristiano Ronaldo's pouting has perhaps played a part in Madrid's stumbles but Mourinho is also under scrutiny after publicly criticizing his team's play, which has appeared meek since beating Barcelona to win the Spanish Super Cup last month.
Mourinho said Monday his relationship with his players hadn't changed after Saturday's 1-0 loss at Sevilla, adding he wouldn't make changes just for the sake of sending a message.
"I will try to field the team that I think will show up," said Mourinho. "I'm convinced that tomorrow I'll have a team out there. Maybe we won't be as relaxed, or filled with the same conviction and confidence we usually have against an opponent like City, coming off a game which was terrible.
"I'm sure we'll be at our best. I could be wrong, but that's what I think."
Madrid's timing couldn't be worse with the Premier League champions visiting the Santiago Bernabeu Stadium to open a tough Group D, in which neither can afford many slipups with German champion Borussia Dortmund and Dutch champion Ajax also in the mix.
There has been little positive to spin from Madrid's start to Mourinho's third season in charge, as all hopes are on the European title since the Portuguese coach has won every other trophy available since his arrival from Inter Milan in 2010.
Mourinho is already downplaying expectations, however.
"The Champions League motivates me as much as the league does. Playing Manchester City motivates me as much as playing Getafe," Mourinho said. "It's like any other game. That's just the natural aspect of my job."
Madrid's home form has at least been spectacular in the competition with only one loss — to Barcelona — in 12 matches, and it scored 24 goals in six games last season. Tuesday's match will present Ronaldo's first return to the Bernabeu since declaring he was "sad" for "professional reasons."
City could have the resources to exploit any lapses with Sergio Aguero available after returning from injury, and fellow striker Mario Balotelli also back. Playmaking midfielder David Villa should start after coming off the bench in City's 1-1 draw against Stoke on Saturday, when former Madrid player Javi Garcia marked his debut with a goal.
Carlos Tevez has scored three goals to continue his City rejuvenation one year after refusing to play against Bayern Munich in the Champions League. That led to the Argentina striker being cast aside for six months, but he has returned stronger.
Mancini even offered Mourinho a lesson on treating his own unhappy star players, suggesting perhaps Ronaldo should follow the same path taken by Tevez and go into exile in his own native country.
"If he wants to try and win the Liga he should send Cristiano to Portugal for six months and then come back," Mancini said from the Bernabeu on Monday. "Last year, it was good because when Carlos came back in January we did very well."
Mancini said Aguero was not 100 per cent but has a chance to play as "it's important if we have a chance we score. A draw could be good result but we don't have this mentality. It's important to start well tomorrow."
Mancini, who is without defender Micah Richards, wants a better start from his team in the competition this time around after failing to get out of the group stage in its debut last season. Mancini dismissed talk of a rivalry with Mourinho, who replaced the Italian at Inter Milan.
"It was a good experience last year, good group, but we did not do enough," Mancini said. "I think we will be more strong than last year. It will difficult for all the teams."
Dortmund, meanwhile, is hoping to make a bigger impact in the competition after finishing bottom of its group on its return to the competition last season.
The Bundesliga champions at least warmed up with a comprehensive 3-0 win over Bayer Leverkusen on Saturday to stretch its unbeaten league run to 31 games.
"That's the football that we want to and have to play if we want to be successful," Dortmund coach Juergen Klopp said ahead of Ajax's trip to Germany. "We've set the bar at where we need to be in the next days."
Ajax will be without striker Kolbeinn Sigthorsson (shoulder), midfielder Eyong Enoh (knee) and defender Nicolai Boilesen (hamstring).
Ajax is undefeated in the Dutch league after five matches with a league-leading 17 goals as it bids to start strong to reach the knockout stages for the first time since the 2005-06 season.
"We're going there full of confidence," Ajax defender Daley Blind said. "We just need to give everything and see how it goes."
Associated Press writers Ciaran Fahey in Berlin and and Mike Corder in The Hague contributed to this report.
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