Manchester City travel to Old Trafford on Sunday as the reigning Premier League champions, but even before the 169th Manchester derby kicks off it seems their hopes of retaining the title are all but over.
Losing to Louis van Gaal's in-form United this weekend would leave City four points behind their local rivals, and a Champions League playoff place far from assured.
So, would such a defeat spell the end for Pellegrini at the Etihad Stadium? Here are some factors, both for and against, which could come into play if Sunday's result is not a good one for City.
YES: City's poor form is worthy of the sack
An analysis of City's recent matches by ESPN FC's Manchester correspondent Richard Jolly has revealed that the club are on their worst run of results since the slump that convinced them to sack Mark Hughes in 2009.
City have lost five of their last seven games in all competitions and they have only won four of their last 14 matches. In late 2009, a run of four victories in 15 attempts led the club to decide to dispense with Hughes' services.
NO: City's hands are tied by FFP
On Wednesday, Gabriele Marcotti explained in a ESPN FC column that financial fair play regulations mean that an overhaul of Manchester City's ageing playing staff will be difficult. The spending restrictions placed on the club by UEFA in 2014 for failing to comply means that attracting a top-calibre coach to the Etihad without the ability to bring in the players they want makes the job a less enticing prospect.
Marcotti wrote: "All of this also means that the Manchester City job is unlikely to be attractive to the kind of instant-fix super-coach the club have been linked with of late, someone like Pep Guardiola, Carlo Ancelotti or Diego Simeone. Even assuming they become available, would they be enthused by the idea of moving to Manchester and basically being told they need to sink or swim with Pellegrini's squad because the club's net spend is capped at $65 million for the next two seasons?
"So what next? My guess is that Pellegrini might end up sticking around. And that City will tweak their squad rather than overhaul it, albeit with more of an eye toward youth. It may mean they end up marginally weaker than this season. But it would be the least risky route and would help defuse some of the problems created by what has been a poorly thought-out approach to squad-building."
- The Sun - Football (@TheSunFootball) April 8, 2015
YES: He has failed to turn his team into serial winners
In the wake of Monday's 2-1 defeat at Selhurst Park, television analyst and former Manchester United captain Gary Neville said: "They have got a mentality problem, there is no doubt about that. This team cannot sustain success, and I think that is a terrible thing to have levelled at you."
Roberto Mancini won the title at City in 2012 but that could not prevent him from being sacked a year later after the club failed to build on that success, finishing as runners-up to United.
NO: It's just his turn in the hot seat
The scrutiny under which managers work has never been greater, with increased attention on the biggest clubs across the globe as millions seek the latest news and talking points.
All it takes is two consecutive poor results and the coach who had just the week before been showered with praise is now on the receiving end of criticism from both media and fans alike.
In his regular Premier League Spotlight column, ESPN FC's James Dall wrote that Pellegrini may simply by at the low ebb of football's regular boom/bust cycle.
Dall wrote: "There is no middle ground -- we deal in the realms of genius or buffoon. That the mild-mannered Pellegrini, whose captivatingly craggy face's arrival to England in 2013 was greeted by scepticism from some quarters, has not come out swinging in the wake of the criticism of his side's latest failing has left him seemingly in a position of weakness. Just how come the Chilean is not roaring on the touchline, or better still throwing off his armless jacket and then embracing a mascot? Instead, speaking after Monday's 2-1 loss at Crystal Palace, he said: 'I'm not concerned about my job. That is one thing I am never concerned with.'"
YES: City have been 'coasting' for too long
Simon Curtis, one of ESPN FC's regular Manchester City club bloggers, saw the Palace loss as an example of how City's players have been coasting for weeks, and the club's hierarchy may feel that a new man in the dugout is the best way to shake out that complacency.
Curtis wrote: "The defeat, slightly unlucky, slightly reminiscent of so many other toothless performances this season, drops them into fourth place in the Premier League table, not a location to make hearts sing nor make Manuel Pellegrini's paymasters cluck contentedly about the future. In fact, if the season closes in a similarly chaotic fashion and an automatic place in the Champions League is not claimed, there is likely to be no Chilean ready to take the club on next August."
NO: Barca too good a match for any side
Aside from turning a title-winning season into an era of domestic dominance, the other major benchmark for success in the City dugout is progress in the Champions League. Mancini was sacked after failing to make it past the group stage two years in a row, something Pellegrini has managed in both his European campaigns.
Unfortunately for him, both times the former Real Madrid coach has seen his City side eliminated by Barcelona in the round of 16, making an assessment of his team's European credentials harder to judge, especially when Lionel Messi turns in the sort of vintage performance that he did in the second leg of this season's tie.
ESPN FC's Graham Hunter wrote from the Camp Nou of that match: "As far as I'm concerned I've been at games in which Messi has won trophies, scored dazzling goals -- four or even five -- and there has been infinitely more 'return' for his brilliance. But it has been a long, long time -- at least a year -- since I've seen him as devastatingly quick, confident, elusive, creative, anarchic and just plain thrilling as he was Wednesday.
"Let's just think about this. Guardiola helped the football boy become the football man of all time and has seen hundreds and hundreds, even thousands, of hours of Messi's best moments, both in training and in matches.
"Yet even he was stunned when he watched this display. Just knocked for six. That tells you what kind of performance this was, regardless of the narrow final score and the fact that it needed Marc-Andre ter Stegen's penalty save from Sergio Aguero to prevent gnawing nerves for the hosts at the end."