As the weeks passed, the nights darkened and Manchester City’s form took an individual and collective nosedive, it was clear some players were struggling badly, none more so than Kyle Walker.

Any City supporter who has watched one of the greatest full-backs of the Premier League era reduced to a shell of his imperious former self in recent months will acknowledge that now is the right time for him to leave the club. Time catches up with everyone eventually, even the best, but Walker’s rapid collapse in form and confidence this season has still been alarming.

It is to his credit that he seems to recognise that as much as anyone, even if football alone is probably not the only factor informing his decision to ask to leave City now. He could have limped on until the end of the season, when he would have entered the final year of his contract with the Premier League champions, but Walker knows his race is finally run at City and there is an element of bravery in facing up to that hard, cold reality.

AC Milan are among those hoping to sign Walker and maybe Italy will be the right home for him – both personally and professionally – as he bids to escape the spotlight and prolong a trophy-laden career beyond his 35th birthday in May and reach that century of England caps he so craves. He is seven appearances short of that milestone.

Discussing Walker’s request to leave in the wake of City’s 8-0 FA Cup win over Salford City on Saturday night, Pep Guardiola suggested the player had reached a point where he no longer feels able to deliver his best for the club.

“Maybe I am wrong but still I am pretty convinced that there is not one person in our jobs – whatever job – that doesn’t want to be where they can’t perform or be what they want to be,” the City manager said.

For the former Manchester United right-back and captain Gary Neville, that moment came against  West Bromwich Albion winger Jerome Thomas on New Year’s Day 2011. Maybe a similar pang of realisation for Walker, City’s long-standing right-back and latterly captain, arrived against Timo Werner and Tottenham in an excruciating 4-0 defeat at the Etihad Stadium on November 23 last year.

Years later, Neville would joke that he made Thomas look like Cristiano Ronaldo and certainly there was a time when Werner could not have hoped to show Walker a clean pair of heels. But it was not just the sight of him being burnt for speed by the Tottenham winger before he crossed for Brennan Johnson to score, it was Walker’s failure to engage sooner, read the danger and shut off the space that felt as significant.

So it may not be a bad thing that Walker is choosing to leave now, but very quickly the discussion will turn to how City plan to replace a player whose very particular skill set helped to provide a cornerstone of so much of the success the team enjoyed under Guardiola over the previous seven seasons.

From David Silva and Sergio Aguero to the likes of Yaya Toure, Vincent Kompany and Fernandinho, City have often moved on seamlessly from the departure of club greats who formed the bedrock of multiple title-winning teams.

In all of those cases, though, their exits were staggered – Toure in 2018, Kompany in 2019, Silva in 2020, Aguero in 2021 and Fernandinho in 2022. Yet Walker could represent the first of a cluster of keystone players to leave in the space of the next six or seven months and that will represent a very different challenge for the club, especially with a new sporting director – Hugo Viana – soon to take over from Txiki Begiristain and the outcome of those 115 charges still to be determined.

Walker, assuming he gets the move he wants this month, could yet be followed out of the door in the summer by the likes of Kevin De Bruyne and Ilkay Gündogan. Beyond that, Ederson, John Stones and Bernardo Silva – all of whom are out of contract at the end of next season – also face uncertain futures and it would not be a surprise if one or two of those left.

City have agreed a £33.6 million fee with Lens for Abdukodir Khusanov but the 20-year-old Uzbekistan defender is a centre-back and the reality is a Walker exit would leave the team exposed in the right-back position, with Rico Lewis the only recognised senior option there. Moreover, Walker’s blistering recovery pace was one of the reasons why Guardiola has felt emboldened enough over the years to play such an aggressive high line with so many bodies committed forward.

It offered a final layer of protection against the counter-attack but without the injured Rodri, and no Walker, City’s vulnerability to the transition is greater than at any point since the Catalan’s first season.

Attempts to characterise Walker as a mere speed merchant have always ignored his other strengths but, beyond the trophies, his career will often be remembered for the relish with which he rose to the challenge of marking players such as Kylian Mbappe and Vinicius Jr, even when he was not always fully fit, too.

Lesser players would have been petrified by the thought of being left one-on-one against such fearsome talents but it became Walker’s brand, his USP. And to think eyebrows were raised at the £50 million fee City paid Tottenham in 2017. It looks a steal now.

Of course, the lurid tabloid headlines sometimes seemed to flow as readily as the trophies – six Premier Leagues, two FA Cups, four League Cups, a Club World Cup and of course the Champions League during that historic Treble season for the record. But, in the main, Walker did not allow what was going on in his personal life to affect his performances on the pitch and there were several instances of him bouncing back from what to some might have been club-ending setbacks.

He could have left, for example, after being omitted from the starting XI for the Champions League final victory over Inter Milan in June 2023 and was courted that summer by Thomas Tuchel at Bayern Munich. But he stayed, played an important role in City winning a fourth consecutive league title and even ended up with the captaincy.

Now, though, he has resolved it is the right time to go. Few would argue otherwise. The problem will be replacing him. There have been few full-backs over the past 30 years to rival him in the Premier League.