The abject nature of City's second-half collapse at Goodison Park opens up the very real possibility that a manager who has reached at least the semi-finals of the Champions League in each of his seven attempts may miss out on Europe's elite competition altogether next season, particularly in light of Chelsea, Tottenham and Manchester United's relentless form over recent months.
The imbalanced, aging squad Guardiola inherited when he took the reins from Manuel Pellegrini in July – only Stoke City, West Brom and Watford had a higher average age this weekend than City's starting XI on Merseyside – appears ill-equipped to improve their lot when Mauricio Pochettino's dynamic, swashbuckling Spurs visit the Etihad Stadium next weekend.
City's courtship of Guardiola was long in the pipeline and severe questions must be asked of director of football Txiki Begiristain, who left his long-time friend from their days playing at Barcelona with a playing group containing obvious flaws when it comes to implementing their boss' famed and highly successful methods.
Nicolas Otamendi arrived from Valencia for in excess of £30million in August 2015, yet the Argentina international's rash tackles and scattergun decision making cast him as the antithesis of the type of measured, playmaking centre-half Guardiola craved.
The coach who once said he would play with 11 midfielders if he could was left with 33-year-old and recent outcast Yaya Toure and 32-year-old career right-back Pablo Zabaleta patrolling central areas against Everton, with key signing Ilkay Gundogan out for the season and Fernandinho suspended.
More generally, the core of this City squad have habitually flattered to deceive since winning the Premier League title in 2013-14 and laying most of the blame with an inconsistent bunch who have failed over two-and-a-half years is probably a more sensible course than stating a football obsessive with ample trophy laden success behind him does not 'get' the Premier League.
Nevertheless, with City's initially promising campaign arguably on the brink of collapse, Guardiola has given himself some tough questions to answer.
HART OUT, BRAVO IN
This is the most obvious stick with which to repeatedly beat Guardiola, and he would struggle to make a case against the validity of a single blow.
His style needs a goalkeeper who can build attacks from the back and Guardiola's capital as a proven winner gave him scope to jettison Joe Hart, however painful it might be for the Etihad faithful to see a long-time fans' favourite plying his trade with mid-table Serie A outfit Torino.
Wanting a 'sweeper keeper' is not Guardiola's problem; it's the one he bought.
Dual LaLiga and Copa America winner Claudio Bravo was at fault for Zlatan Ibrahimovic's goal past him on his debut in September's Manchester derby and, although City held out to win 2-1 at Old Trafford, he has resoundingly failed to inspire confidence ever since.
Everton's four goals from as many shots on target on Sunday meant Bravo has let in 14 of the past 22 shots on his goal in the Premier League. The 33-year-old's save percentage of 57.4 is the third worst in the division, while he has only four clean sheets from 18 starts.
Meanwhile, in Italy, Hart has a save percentage of 70.5, with more catches and fewer drops than Bravo this season. His pass accuracy is down on the Chilean's – 71.5 per cent to 64.5 – but there is a galling footnote to this category.
In Hart's apparent City farewell against Steaua Bucharest in August, the goalkeeper who could not use his feet found a team-mate with every one of his 16 passes.
Guardiola made Stones the most expensive defender in Premier League history when he arrived from Everton in August and the England man's fortunes have mirrored his manager's to date.
Stones featured in every game as City flew out of the blocks with 10 wins from their first 10 matches this term. Both player and team have since struggled to convincingly relocate their poise.
The 22-year-old's commitment to picking passes, dribbling and occasional Cruyff turns has prompted a stifling interest in his work that often moves rapidly from curiosity to distain.
Stones played a vital role in City's best football this season and has offered plenty of glimpses of the undoubted talent that has persuaded club and international managers to tolerate the blemishes.
Unfortunately, these are blemishes that are becoming more frequent as City falter – his three errors leading to goals this season represent a league-high figure – and a player with a near-£50m price tag and 94 Premier League appearances to his name can only hide behind inexperience to a certain extent.
Given the relentless debate over whether Guardiola's approach can work in the Premier League, signing the unconvincing poster boy for everything English centre-halves are not supposed to be at eye-watering cost has invited unnecessary additional scrutiny.
A regularly stated and simplistic criticism from the Guardiola naysayers is, 'you can't play Barcelona football at Man City'. In fact, it is the 45-year-old's extension of the methods he honed during three years at Bayern Munich that are getting him in over his head.
As Barca boss, Guardiola deployed a familiar and fluent 4-3-3 system, occasionally switching between this and 3-4-3 later on in his tenure. At Bayern, with a supremely well-tooled squad at his disposal, he shuffled through a vast array of tactical shapes.
In simple terms, his players at City are nowhere near as good. The sight of Zabaleta giving everything for the cause in midfield further endears a popular and selfless player, but a Philipp Lahm conversion from full-back to lynchpin is entirely unlikely.
This does not mean Guardiola's current band cannot strike up a tune. Deployed in a 4-1-4-1 variant of 4-3-3 over the first 10 games of the season, they played some spellbinding stuff – David Silva and Kevin De Bruyne wreaking havoc from central areas, Raheem Sterling motoring down the flanks and Sergio Aguero collecting fistfuls of goals.
A deserved 2-0 loss at Tottenham, where Pochettino read and clinically took down his gameplan, seemed to spook Guardiola. Home draws with Everton and Southampton featured a 3-2-4-1, matching Chelsea's 3-4-2-1 ended in a 3-1 loss and a 4-4-2 diamond beat West Ham 5-0 before shattering at Everton. What City were attempting to play in the opening stages of their 4-2 loss at Leicester City is, frankly, anyone's guess.
One Bayernism from the opening days of the season did serve Guardiola well and should be revisited. Inverting his full-backs into defensive midfield roles while in possession was an effective ploy when it came to cutting off counter-attacks at source. Now, opponents rarely seem more than two passes away from Bravo's flimsily kept goal.
Tearing pages out of his vast playbook and relocating the simplicity of late summer might be Guardiola's swiftest route to rehabilitation.
A striker with 18 goals from 23 appearances this season is a problem many managers would love to have. But something is amiss with Aguero.
Guardiola neglected to unreservedly praise the Argentina star after he scored his second Champions League hat-trick of the campaign against Borussia Monchengladbach in September. There were similar 'he's good, but' sentiments following a brace at Swansea City later in the month.
Six scoreless appearances followed, including three from the bench – most notably when Guardiola omitted the club's premier attacker from the starting XI to face Barcelona.
Since Camp Nou, Aguero has a less prolific seven in 13 appearances and served a four-match ban for a second offence of violent conduct this term. The 28-year-old, synonymous with a cheery smile, has cut an unusually frustrated figure and again appeared to be unravelling during the torturous closing stages at Goodison.
While not as complete as other forwards he has managed, Guardiola has an elite penalty box operator on his hands in Aguero.
Ambitions to add further strings to his bow are in line with the coach's ideals, but, with City lacking badly in other areas, turning proven performers into pet projects – also see De Bruyne's deployment on the left of a midfield diamond recently – is an indulgence Guardiola cannot afford.