John Stones is perhaps the only Manchester City player who is having an up-and-down season. Yaya Toure, curiouly, is simply out of the picture but Stones' young team-mates are improving and his older ones are playing the best football of their career.
Stones looked as impressive as the rest in the first part of the season, but since his return from injury in January he has been out of form and, it is said, low on confidence.
The young Englishman, subject of so much attention on these shores given his unorthodox, forward-thinking approach to defending, struggled in his first year as a City player.
While he was often exposed by his team-mates as Pep Guardiola's plans took their time to take hold, he was also guilty exposing those around him with a mistake or poor decision-making.
Sources close to the City coaching staff were concerned about his mentality last season, worrying that he would dwell so much on his past errors that it would affect his future performances. Guardiola would never even hint at that in public and in fact he once praised the size of Stones' "balls", pointing out that his centre-backs need to defend huge spaces, usually against quick players, as well as take risks in dangerous areas to start attacks with their passes.
In the early stages of this campaign, that is exactly what he was doing. He and his particular set of talents finally looked at home and he was proving that he was being improved, not indulged, by Guardiola.
In the absence of Vincent Kompany, and following City's failure to bring in another centre-back during the summer, Stones formed a fearsome partnership with Nicolas Otamendi.
The two had previously failed to impress when deployed together, but between September and December they were the solid foundation on which Guardiola's new-look City were built. A source close to the City boss has described Otamendi's transformation as "second only to that of Philipp Lahm from full-back to midfielder", owing to his new-found passing ability, but in Stones' case it just looked like he was fulfilling his potential.
Not only was he consistently demonstrating his eye for a killer pass and the ability to play it, he was doing the dirty work in defence, too. He looked strong and assured, while the mistakes and misjudgements were a thing of the past.
He was playing so well that it was regarded as a major blow when he was ruled out for six weeks with a hamstring injury at the start of December.
City, as they have done in other areas, managed to cope without him and they have continued their fine form well into 2018, but Stones has not looked the same dominant force since he returned two months ago and in many of his performances he has committed errors which have led either to goals or near-misses.
Against Burnley in the FA Cup, he sliced at a clearance which allowed the visitors to take the lead. In the next game, against Bristol City, he conceded a rash penalty. Next, against Liverpool, he misjudged a ball in behind which allowed Roberto Firmino to put the Reds 2-1 up, sparking a wild nine-minute period in which City collapsed and conceded three goals.
In his most recent game, against Wigan, he was not at fault for the fateful goal which put City out, but twice in the first half he looked decidedly unsure of himself, standing off when he could have closed down and then, after jockeying backwards for about 40 yards, not being able to put in a block anyway.
Not that Guardiola would let that slip in public. Quite the opposite, in fact: "John is an extraordinary player, what he has done has shown me that," the Catalan said on Tuesday. "Now we have four excellent central defenders, Vincent Kompany for a long period was not able, now he played in the last games, and of course the last game John had a chance [to play], the next game he has a chance. I don't know what it's going to be. But we don't have, I don't have, he doesn't have any doubts about his capacity, his ability to play in this team."
Guardiola also explained that he plays Kompany and Otamendi together, as he did twice against Arsenal, because they are "both amazing at winning duels". Aymeric Laporte started against Chelsea because, the Catalan says, the Londoners could have used two systems, ones which required a versatile, left-footed defender to combat them.
In short, City have options now. For the first time Guardiola has four fit, top-class centre-backs to choose from, and Stones, after two months of patchy form, has to prove again that he can do the job as well as the others.
He has shown already this season that he can live up to his vast potential, and if he can stay at that level it would be no stretch to suggest he can become one of the best centre-backs in Europe. But before he can scale those heights he needs to force himself back into the City first-team.