It is all about the full-backs but these days it is always all about the full‑backs. From a tactical point of view Sunday’s meeting between Liverpool and Manchester City is likely to be settled by Trent Alexander-Arnold against Aymeric Laporte and Andy Robertson against Kyle Walker – and, if it is not, it will be because Pep Guardiola has chosen not to take on that fight. Jack Charlton’s observation after the 1994 World Cup that full-back had become the most important position on the pitch seems wiser by the day.

Full-backs, Louis van Gaal insists, are the key to Guardiola. The biggest difference between the football he practised with Guardiola in his midfield at Barcelona in the late 90s and that played by City now, he said in an interview for The Barcelona Legacy, “is that a lot of times he has two full-backs in front of the central defenders. Guardiola takes a big risk and that’s why he can lose. The space behind is too big for the central defenders and he doesn’t have such fast central defenders.

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“I always had it so that when the right full-back is going up, the left‑back has to squeeze. The problem [for Guardiola] is that the space behind the defence will be bigger. You can exploit that when you have individual players who can play under the pressure of Manchester City. Liverpool did it – a pass to Salah or Firmino and then they are gone.”

This explains the apparent paradox of City conceding the fewest goals in the league last season and yet at times – notably twice at Anfield against Liverpool, in the second half at home against Manchester United and at times in the Champions League away at Shakhtar and in both matches against Maurizio Sarri’s Napoli – looking defensively suspect. They stifle opponents by keeping the ball from them but can struggle against opponents who are not overwhelmed by their press.

Guardiola has reportedly been working on shapes and new patterns of play as he seeks further progress in the Champions League but little in the group games so far suggests the problems have been resolved. Lyon unsettled City by pressing them and forcing them into mistakes; Hoffenheim attacked the familiar vulnerabilities between central defenders and the full-backs.

It was presumably an awareness of that potential flaw that led Guardiola last season to leave out Raheem Sterling and deploy Ilkay Gündoğan in a withdrawn role on the right in the first leg of the Champions League semi-final. That would protect Walker and help City keep the ball and control the game, to prevent Liverpool generating the head of fury that had brought three goals in nine minutes in the league game at Anfield three months previously.

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That sort of change is a Guardiola trait, a strength that can become a weakness. Part of his genius is his constant flexibility and his willingness to adapt but there are occasions when he seems to overthink things. He will be aware that Jürgen Klopp is the only coach he has faced on more than three occasions who has a positive record against him and that could prompt a change.

If there is one, it is likely to come in midfield, if only because of the lack of options to play as a left wing‑back. With Benjamin Mendy and Fabian Delph injured, the most likely candidate to play on the left of the defence is Laporte. It is one thing to press a mobile central defender into service as a left-back, quite another to make him play as a wing-back. There is the option of using Leroy Sané as a wing-back but even for Guardiola that is probably too bold a step.

Yet Liverpool, too, seem to have been concerned by their full-backs. Neither Alexander-Arnold nor Robertson has been as attacking this season as they were last and, while that may have brought a greater sense of defensive stability, it has equally had an impact on the effectiveness of the wide forwards.

It would be unrealistic to expect Mohamed Salah to reproduce the sort of glorious form he enjoyed in the first quarter of the year entirely consistently, and there are numerous reasons why he may not have looked quite so threatening this season as he did last but one of them is that he no longer has Alexander-Arnold hurtling outside him every time he gets the ball and distracting the full-back to allow him to cut inside to attack the defender on his weaker foot.

Both sides, then, face a similar issue. Both have benefited from the potency of their full-backs but are aware there may be benefits in having them play a little more conservatively. If it is 4-3-3 against 4-3-3, whoever better manages the balance in that area should have the edge.