How long does it take to go from invincibility to fragility? From looking like the greatest team of their generation, to merely the third best team in the league.

That has been the story of Manchester City’s December, as they have picked up three points from four Premier League games, their worst run since March/April 2017, back when the squad was half as good and the players were still struggling to come to terms with Pep Guardiola’s methods.

Going into this month, City looked dominant at the top of the table, playing as well as ever and with squad depth and experience that would ultimately give them the edge over Liverpool. And while their defeat at Chelsea was the type of loss a good team should be able to stomach, losing to Crystal Palace and Leicester City were double disasters, defeats that point to something having gone profoundly wrong for the Guardiola project.

Any team can lose a game, but this is a team that broke all the records last year: 100 points, 106 goals, 32 wins. They were pursuing perfection, and had got further than anyone else. And after 15 games this season, they had won 13 and drawn two, away at Liverpool and Wolves. Talk of another title, a treble, Invincibility, it all felt ahead of this team if they could hold off Liverpool’s challenge. Until this month the sky fell in.

Yes, Guardiola can talk about how City keep conceding from the first shot they face each game. And he is right: that has happened in three of their last four league games, turning the momentum against them in games they had under control, against Chelsea, Crystal Palace and Leicester City. But how many times does a fluke have to happen before it becomes a trend?

Earlier this season, City had the tightest defence in the country. Not only were they conceding fewer shots than anyone else, they were conceding fewer shots than any other team in Premier League history. By the end of November, City were conceding just 1.92 shots on target per game, which would have been the lowest number ever recorded, even better than Rafa Benitez’s Liverpool side of 2007-08 who conceded just 2.29 shots on target per game. City’s control looked so total they were impossible to hurt.

But that security has evaporated quicker than anyone could have expected. For this City team, defending relies not on building a wall in front of their goal, but on maintaining a constant pressure, never allowing the opposition that yard of space to attack. But the problem with that approach is that it is as fragile as a pack of cards. One imperfection or error and the whole thing falls apart.

That has been the story recently, especially with the absence of Fernandinho in holding midfield. He is not City’s best player, but he might be their most important, the man who allows seven of his team-mates to attack together, stopping any counter-attacks as well as getting City’s own passing moving briskly forward. He is the keystone of this City team, bearing the whole weight of the structure. Remove him and the bridge collapses.

So it has proven in the last few weeks, as City have run headfirst into the limitations of being utterly reliant on a 33-year-old who has been playing at full pelt for years and who cannot be expected to keep doing two games a week into the indefinite future. None of the possible replacements are anywhere near good enough. John Stones is not a midfielder, Fabian Delph is not disciplined enough and Ilkay Gundogan is not physical enough to defend.

So what is the solution? How City must wish they had signed Jorginho in the summer, to give them the option of another tactically intelligent midfielder who could anchor the rest of the team while starting City’s attacks. They have been seriously interested in Frenkie De Jong but he is unlikely to leave Ajax next month, and other teams have moved ahead of City in the race to sign him.

And so City are left anxiously watching Liverpool and Spurs’ games on Saturday, hoping that when they get to Southampton on Sunday afternoon they will even have Fernandinho ready or some new solution to that midfield problem. Because they cannot afford to drop even further behind Liverpool before Jurgen Klopp’s side come to the Etihad Stadium on Thursday night. They are in a spiral and if they do not snap out of it they will not achieve what was hoped for them this season.