John Stones was supposed to be Man City’s best defender by now – so what happened?

How young is young? Roy Hodgson used the word, but he is old, the oldest manager in Premier League history. Gary Cahill used it too but he is relatively old, the 12th oldest outfield player in the division this season. John Stones is not old but, turning 26 in May, with 39 international caps and almost 250 club appearances to his name, he is scarcely as young as his former England manager and teammate seem to think.

The temptation is to assume those in the first half of their careers are works in progress, but Stones has regressed this season. Age can equate to promise, but the promise of a brighter tomorrow is not always realised and potential is not automatically translated into performance. Certainly Stones’ display against Hodgson and Cahill’s Crystal Palace was not that of a man on an upward curve. He might have conceded a penalty for a clumsy first-half challenge on Wilfried Zaha. He was unable to halt the winger when Zaha surged past him to set up Palace’s last-minute equaliser in a passage of play Pep Guardiola called “a mistake”. In between, he was out-jumped by Cahill when the best centre-back on the pitch set up Cenk Tosun’s opener.

“I still think that John Stones is every bit what we expected him to be,” said Hodgson. “John’s young, too. He still has his best years ahead of him.” Cahill echoed: “He is still young, if you look at his age. He has still got his best years ahead of him.” And, in theory, he does.

“He’s still learning the game,” Hodgson said. “If he stays fit I’m sure he’ll progress under this manager,” Cahill added. But the manager in question, Guardiola, can be gnomic on the subject of Stones. Had he got his wish and signed Harry Maguire in the summer, had Aymeric Laporte stayed fit, he would have been an expensive understudy. As it is, Fernandinho has been City’s finest centre-back this season. He is in his 35th year but, as a converted midfielder, he is young as a defender.

It was the Brazilian’s late own goal that cost City victory. However, Stones was more culpable. Hodgson, a manager who prefers life outside the limelight, where his every decision is not scrutinised, said: “He’s playing in a very important goldfish bowl at the moment. Every mistake or every good thing is magnified 10 times over.”

Hodgson has long seen himself as a voice of moderation, but Stones’ moderate form is the issue. He was in a better state 12 months ago, fresh from the goal-line clearance against Liverpool that proved decisive in the title race. In each of Guardiola’s two title-winning seasons, Stones excelled in the first half but made way for Vincent Kompany in the run-in; the fact the captain was preferred when it mattered most suggested he does not command his manager’s full confidence.

Perhaps Gareth Southgate has more faith than Guardiola, even if time will tell if it was undermined by the extra-time error that helped Holland reach the Nations League final last year. Cahill harked back a further 12 months to Stones’ peak to date. “He had a fantastic World Cup,” he said. “What you have to remember is on one of the biggest stages he was terrific.”

It was the greatest advertisement of Stones’ talent. Now, however, his development feels arrested. A pass completion rate of 93.9 percent is both off the charts and Guardiola-esque but questions about his defending persist; he is yet to become a figure of Cahill-esque solidity. Injuries have made it a stop-start season, but City have only won on three of Stones’ last seven starts; one of those was against Port Vale and they have conceded 11 times in those seven games.

As Guardiola noted, Palace had few opportunities and got two. “They didn’t need much to score goals,” he said. “We have to improve.” An upgrade may soon be available, with Laporte back in training. “We cannot expect that Aymeric is going to solve all of the problems,” Guardiola added. But it will compound Stones’ problems if the Frenchman’s imminent comeback is at his expense. Laporte feels the senior figure at the back, but he is only one day older than Stones. And Stones isn’t young anymore.