City's underwhelming 2015 took a considerable turn for the worse as they were overpowered by their arch-rivals in a 4-2 defeat at Old Trafford.
Their Barclays Premier League title defence was already looking over but that result has potentially left their campaign in ruins and prompted much criticism and soul-searching.
City have won just four league games from 12 since jointly leading the table in early January and any more bad results could put their top-four place in jeopardy.
The pressure on Pellegrini and his players, with rumours of a potential clear-out in the summer, is considerable and they badly need a victory as West Ham visit the Etihad Stadium on Sunday.
Pellegrini said: "When you lose a game the first few days are always difficult, especially when you lose a derby.
"But I think the players are conscious we don't have results that we deserve
We continue being the team that scores more goals.
"We defended very badly in the last game but we have the fifth (best) defence in the Premier League
We are the team that always have the most possession in every game.
"We have to be clear why we are not having the most results, which mistakes we are making.
"Two or three balls change the performance of the whole team, so it is very important to have the correct 'diagnostic' about the team, about what we must change, what we must do in the future."
City were beaten 2-1 at Upton Park in October, a result that was unexpected at the time even though West Ham were in form and flying high in fourth.
After that game, Hammers boss Sam Allardyce suggested that City had become predictable and that is how his side had managed to outmanoeuvre them.
That has been a familiar criticism of Pellegrini and his tactics since, particularly as City have stagnated in recent months.
Pellegrini is well aware of this but remains steadfast in his methods, insisting that the problem is in the execution and not the lack of variation.
He said: "Every manager knows how we work, how we play
The problem we have this year is that we've scored 21 goals less, it's not because we are not creating chances.
"If we never created chances maybe we'd change the system but we always do
We are the highest scoring team of the Premier League.
"The diagnostic is not that
There may be a lot of different diagnostics why it's not happened."
Pellegrini is also well aware that his team cannot afford to miss out on Champions League qualification
That would be a serious blow to the ambitions of the club and quite possibly make his position untenable.
But Pellegrini said: "I don't think in a negative way
We are still in the Champions League places.
"It's easy for a big team not to be in it - United last year
There are four or five strong teams here
"
West Ham manager Sam Allardyce is not bothered by how Manchester City will react to their slump, only that his own players produce the goods at the Ethiad Stadium.
West Ham are also in need of some consistency, with a stoppage-time goal conceded at home to Stoke denying them what would have been only a third league win of 2015
"I am more concerned about getting the best out of my team," said Allardyce, whose side are now in 10th place, having once looked set for a European qualification challenge themselves.
"Maybe City are a wounded animal and they might come out all guns blazing or they might be tentative
We won't know until the match starts.
"We are expecting them to put in a determined performance in front of their own fans."
Allardyce added: "The motivation for our players should be that they have let themselves down by not achieving the results that they should have done from the positions we have been in.
"We want to get the feel-good factor back by winning a few games and getting the confidence back up."
Allardyce believes the Irons can yet go on to secure their best finish since winning promotion back to the top flight.
"At the moment we want to reach the 50-point mark or higher, that will make sure we finish higher than we have done in the three years we have been back," he said.
West Ham will be without Senegal forward Diafra Sakho because of a thigh strain, but Enner Valencia has recovered from a foot problem and so will lead the front line alongside veteran striker Carlton Cole.
Source : PA
Source: PA