City cut United's lead at the top to five points on Wednesday and will slash it to two if they win at Carrow Road.
However, Mancini is wary about the trip to East Anglia which comes just three days after the win over West Brom.
"United is easy," he said.
"We could lose or we could win but it is an easy game. Against United or Chelsea, our concentration will be 100%.
"Norwich will be really tough because we have only had two days to recover after West Brom."
It seemed Mancini had his tongue firmly lodged in his cheek as he delivered the comments.
Indeed, his entire press conference was conducted in that confusing manner as he backed the comments of United assistant manager Rene Meulensteen that the Red Devils have greater togetherness.
"I agree with him," said Mancini.
"They have big experience and are a fantastic team. We are nothing.
"But sometimes the best team, or the team that has balance, doesn't win."
"But I am proud of my players for everything, including our mistakes.
"We are not on the moon. We are normal, like all normal people we can make mistakes."
Meanwhile, Mancini also confirmed midfielder Yaya Toure could be available tomorrow [Saturday] despite missing the midweek win over West Brom with a knee injury picked up during last weekend's defeat at Arsenal.
"Yaya is getting better," said Mancini. "We will decide tomorrow [Saturday] but there is a chance he could play."
There is little doubt the Blues are a more formidable side when Toure is available, yet Mancini still doubts whether City can overhaul the Old Trafford outfit.
"It is very difficult," he said.
"That doesn't mean we don't want to try or we don't have a small chance to win.
"But I hope we play like we did until three or four weeks ago, not how we played against Arsenal."
Although a reputation for considered decisions has grown around Sheikh Mansour and chairman Khaldoon al-Mubarak in their dealings at City, they proved how quickly they were prepared to act by axing Mark Hughes two-and-a-half years ago.
Yet Mancini does not feel the end-of-season judgement will be a harsh one, pointing out that, while City have spent huge sums in recent years, it has been done with the idea of building for the long-term rather than merely a quick fix.
"When I arrived here the owners told me they wanted to go in the Champions League and fight for the title in two or three years," he said.
"After one year we finished third with Chelsea and won the FA Cup.
"In the second we have fought for the title until now.
"All the time, people say we have spent money. But it is only like the other teams. In the last seven or eight years, they have spent £400-£500million as well.
"We didn't buy Cristiano Ronaldo, Lionel Messi or Andres Iniesta.
"If we bought Messi, we should win. We would have a player who scored two goals in every game.
"But we bought young players who need to improve together."
In any case, Mancini would view a second place finish as a step forward, even if it is less than it seemed likely they would achieve for so long.
"We should be proud of the job we have done until this moment," he said.
"It is our best season since 1968, when Manchester City won the championship.
"We have a serious owner and serious chairman. They understand this. People who are very serious do not think if we lose two or three games they want to change everything.
"And if we had a bad season, what about the teams who are 10 or 15 points behind?"
In the immediate aftermath of Balotelli's dramatic appearance at Arsenal on Sunday, when he was sent off for two bookable offences and could have received a very hefty ban for a tackle on Alex Song that even Mancini admitted warranted a red card, the City boss said his young striker would be sold in the summer.
Balotelli has since apologised, claiming he remains committed to the Blues and does not want to go anywhere.
Mancini has accepted the words.
However, as Balotelli serves the second game of his three-match ban against Norwich tomorrow, the City manager indicated Balotelli's actions are of more value that mere words.
"We are happy but it doesn't change the situation," said Mancini.
"If he wants to stay he should change his mind.
"I spoke with Mario a lot of times about this.
"I don't think he can stay here for 10 years together with me. This is impossible. But if tomorrow, or in two or three years, he changes managers or squads, it is important he changes his behaviour.
"He has a lot of quality but he can lose it with his attitude."