As Liverpool supporters prepared to celebrate Christmas, they must have thought that the worst of the 2020-21 season was behind them.
Basking in the afterglow of a thumping 7-0 victory over Crystal Palace, the Reds were four points clear at the top of the table a third of the way through the campaign, with just a single defeat to their name.
That 7-2 loss to Aston Villa was already looking like an anomaly they would be able to laugh about once the successful defence of their title had been completed.
But nobody escapes the turbulence of pandemic football.
Liverpool have scored just one goal in four league games since their victory at Selhurst Park, and having failed to win a single one of those matches now find themselves fourth in the table.
It is too early to talk of crisis, but Liverpool fans will be worried by Manchester City’s growing confidence and slightly panicked by the fact Everton would have a chance to go above them were they to win their game in hand.
But what has caused such a dramatic change of fortune?
The most likely explanation for the slump is that an injury crisis, coupled with the effects of Covid-19 on the tactical landscape of the Premier League, have combined to disrupt Jurgen Klopp’s attacking plans.
But we must also tentatively ponder whether their form is an early sign of lasting decline.
Losing Virgil van Dijk and Joe Gomez to long-term injuries has indirectly impacted upon Liverpool’s ability to maintain the attacking dynamism that made them so ruthless last season.
The Reds' success over the last two years was built on relentlessness in possession, as sustained attacks over an extended period of the match eventually ground down the opposition.
Klopp’s side would pummel teams with wave after wave of pressure that either built through the middle or, if that avenue was closed off, via their overlapping full-backs.
A lot of this incessant pressure has, though, diminished since Jordan Henderson and Fabinho have been removed from midfield to fill in at centre-back.
In two of their last four Premier League matches, both have been deployed at the heart of the defence, while in the other two Henderson played as the holding midfielder, meaning neither player has featured in their best position throughout this winless run.
Fabinho’s usual screening role as the deepest midfielder cuts off opposition counterattacks at source, keeping the opponent penned in for those waves of pressure, while his excellent long-ball distribution also helps to push teams into retreat.
Henderson’s energy and purposefulness as a box-to-box midfielder, meanwhile, drives Liverpool forward, setting a high tempo and ensuring the ball is perpetually forced into the final third. Lest we forget, the decision to reposition the Liverpool captain in a more advanced role proved to be one of the final pieces of Klopp's jigsaw back in 2018.
Without these two in midfield, Liverpool cannot maintain pressure or speed of play, instead conceding territory on the counterattack and getting drawn into plodding matches with few clear-cut chances.
Furthermore, when Liverpool are not camped in the opposition half or probing for long periods, their full-backs Andrew Robertson and Trent Alexander-Arnold cannot afford to sit so high up the pitch. Without Fabinho screening they need to be more wary of the counterattack, hence their decreasing influence.
When Robertson and Alexander-Arnold spend less time in the final third, Liverpool lose the option of stretching the opponent, leaving them too narrow and one-dimensional when attempting to score.
Klopp’s model is built on an impossible-to-defend dual threat: if you go narrow, we go wide; if you go wide, we go narrow. Indirectly, that threat has diminished since the midfield linchpins were removed.
Ordinarily one would expect Klopp to find solutions to the problem, even with a mounting injury list that means the misfiring Roberto Firmino has to play every game.
But Covid-19 has dramatically reduced time to coach in the week, which along with a truncated pre-season and exhausting schedule has seen teams slog through games without much tactical cohesion.
Like all of their rivals, Liverpool’s pressing intensity has dropped significantly and there is no time for Klopp to implement a new system.
Add all of these factors together and you get a tired team with fewer attacking outlets playing at a lower tempo and without the personnel to implement their usual method of suffocating the opposition into submission.
Throughout their two-year blitz of brilliance, Liverpool’s margins of victory were slim. Last season they over-performed their expected goals (xG) and expected goals against (xGA) to accrue an astonishing total of 24.72 extra points, per understat.com, and so it only takes a minor downturn in that relentless pressure for the goals to dry up.
Those xG figures have always been a slight cause for concern, giving the impression of a team riding a wave of momentum rather than one obliterating their opponents as Manchester City did in their title-winning seasons under Pep Guardiola. There was always the worry that it would only take a slight knock for Liverpool to drop off a cliff.
It is important not to over-react to what is, after all, just a four-game run of poor results. Nevertheless, it is worth tentatively questioning whether Liverpool, who have followed Klopp’s Borussia Dortmund era so closely, will eventually come apart like the manager’s last project did.
His Dortmund and Liverpool teams are both emotional, both built on a groundswell of feeling that drives the press and that drives them to narrow victories week after week. As at Dortmund, things suddenly clicked for Liverpool – they had their “boom” moment, as ex-BVB defender Neven Subotic put it in the book 'Klopp: Bring the Noise' – and, as at Dortmund, perhaps things will end just as quickly.
After all, Firmino, Mohamed Salah, and Sadio Mane will all turn 30 at some point next season. The physical and emotional energy expended at Dortmund eventually led to exhaustion. Watching Liverpool’s three forwards linking so poorly over the last four matches has made it easier to imagine something similar happening at Anfield.
There is little to suggest Liverpool are approaching this stage, but should they continue to out-perform their xG, and should the injury crisis continue for much longer, then eventually the point will be raised.
For now it is a case of getting Firmino firing again, lifting Alexander-Arnold’s spirits, and finding a way to rejig the starting XI to fit Fabinho and Henderson back into their best positions.
These are only minor tweaks. But as we have seen over the last month, at a club as fine-tuned as Klopp’s Liverpool the smallest of changes can have a butterfly effect.
The margins are razor thin – and in this season more than ever.