The Blues are reeling after their catastrophic Champions League defeat to Ajax on Wednesday that has left them needing a 'miracle' to avoid a group stage exit for the second season running.
Four points behind Premier League leaders Chelsea and already out of the Capital One Cup, the reason for City's failings is easy to spot; their previously watertight defence cannot stop leaking goals.
They have now conceded 22 times in 13 games in all competitions, eight fewer than the time it took last term.
City have a single clean sheet to their name, compared to five at the same stage 12 months ago.
So, whilst Mancini is refusing to get too down about the situation, evidently he sees problems that need to be solved.
"At this moment we don't have a best defence," he said.
"For two years we were the best defence in the Premier League. At this moment no.
"We are not playing very well with the defenders. We need to work hard and we need to improve."
What Mancini will not accept is his much discussed three-man defensive formation having anything to do with it.
Micah Richards courted controversy in Amsterdam when he claimed the City players were ill at ease with the system, but that Mancini insisted on using it in preference to the more orthodox four-man back-line.
"In pre-season we only had 10 senior players," he said, ahead of Saturday evening's encounter with Swansea at the Etihad Stadium.
"But I wasn't changing anything. It is difficult to watch from the stand when we change the system but we have used this a lot of times during games last season, a minimum of 50 times.
"We were 2-1 down and we wanted to improve the situation.
"With this system we beat Chelsea 3-2 in the Community Shield. With this system we recovered from 3-0 down against United, got back to 3-2 and had a chance to draw with only 10 players.
"With this system we have changed the result every time."
Not this time though. And Richards' post-match comments appeared to challenge Mancini's authority.
That is not the Italian's view of things, even if his own assessment of the situation is fairly straightforward.
"I talk with the players - with my hairdryer in my hand," he said.
"They can talk to me about anything, the tactics, everything.
"What Micah said is not important. He was asked one stupid question, when he was tired after a game.
"But good players should be able to play in any system.
"If you are a top player, the system is not important. If you don't understand you are not a top player and you cannot play for a top team.
"Maybe Micah doesn't know this because it is his first game. He has been out for two and a half months and has worked less than the other players.
"Maybe the next time we play this system Micah can stay on the bench and we will play with another player."
Mancini is determined to get City's season back on track, even if Europe once again appears to be a step too far.
"I am not frustrated about what people say," he said. "It is not a problem for me.
"I have my own opinion about everything. Sometimes I make mistakes, like the players, like the owner, like everyone.
"But I work hard every day and when you work seriously you don't have any problem about your job.
"You think we can go down after one defeat? I don't think so. We are strong enough for this.
"But, whilst it is not easy to win the Premier League, in order to stay on top for a long time, we need to work even harder than last year."