It was two years ago on Wednesday that Argentina won the World Cup. England had gone out to France in the quarter-finals and, beyond the usual kneejerk attacks on Gareth Southgate, there was a sense of general optimism. They had lost in a 50-50 game, beaten in the marginal details, and the squad looked young and fresh. When had we last seen an England attack so bristling with talent, as a front three of Bukayo Saka, Harry Kane and Phil Foden demonstrated, with Raheem Sterling, Jack Grealish and Marcus Rashford on the bench to replace them?

How quickly the world of football changes. Grealish is an intermittent presence at a glitching Manchester City. Sterling, chewed up by the Great Disruption at Chelsea, has vanished on his loan at Arsenal. But nobody perhaps has suffered a more striking decline than Rashford. He’d scored off the bench against Iran and got two against Wales on his only World Cup start in Qatar. He returned from the tournament in the form of his life. He scored eight goals in his next seven appearances. In total that season, he scored 30 goals for Manchester United.

1:55

'We're better with Marcus Rashford': Ruben Amorim addresses United exit talk around player – video

He’d campaigned successfully to secure free meals for disadvantaged children during school holidays, which appeared to speak not only of a social conscience but unusual maturity. He seemed to have added a yard of pace and a greater directness to his game, and had a pleasing knack of putting the ball in the net. By the end of that season, he was 25 and seemingly entering his peak.

Since then he has scored 11 Premier League goals. When he was left out of England’s squad for the Euros, the reaction was less of dissent than sad acceptance that, on form, and given England’s strength in depth, it was probably the right decision. Then, on Sunday, came what may turn out to be a decisive moment as he, along with Alejandro Garnacho, was omitted from Ruben Amorim’s squad for the Manchester derby.

The reasons weren’t entirely clear with Amorim saying: “We try to evaluate training performance, game performances, engagement with teammates … I pay attention to the way you eat, the way you put [on] your clothes to go to a game.”

The last sentence in particular has been subject to intense analysis. Was he talking about dress sense? And if so, was that part of the uncomfortable coding so common in football? While it’s impossible to know for sure, in context, particularly given Amorim stipulated it was “the way” players eat and get dressed in general rather than necessarily what one individual eats or wears, it appeared he meant he assesses every detail to see how focused a player is.

Even so, the suggestion Rashford is not as engaged as his coach would like him to be can hardly have come as a surprise. In his third game back after the World Cup, although he scored after coming on at half-time, Rashford was left out of the starting lineup for a league game at Wolves having overslept and missed a team meeting. Since then there has been a semi-regular drip of hints that he struggles to take on board tactical information as well as stories about ill-advised off-pitch decisions, notably trips to Belfast and the US. Players have every right to relax – and should relax – but there is an impression of somebody increasingly disillusioned by life at United. Which, up to a point, is reasonable enough.

Rashford has been shunted around, playing on the right and through the centre as well as on the left. He’s often been left out altogether. While his lack of form is partly responsible for that, nobody could claim the club over the past few seasons has been a stable or encouraging environment. A certain disillusionment is inevitable, perhaps especially for a local lad who has an emotional as well as financial bond with the club.

Kick off your evenings with the Guardian's take on the world of football

after newsletter promotion

Amorim, sensibly, has said nothing to indicate the club may be looking to offload Rashford, nothing that may further lower his value. But, equally, it’s not really clear where Rashford fits in his 3-4‑3. It has become clear that his best role is cutting in off the left, but the left-sided forward role in an Amorim team needs to be filled by a technical player who can drop off and link with the midfield, which is not Rashford’s strength. At least in terms of starts, Amorim had used him as a centre-forward and off the right before giving him the inside-left role in the Europa League win against Viktoria Plzen. Rashford said on Tuesday he thinks that is the role to which he is most suited, but he disappointed in the Czech Republic and was withdrawn 10 minutes into the second half.

Rashford’s comment this week that he is “ready for a new challenge” is probably the inevitable endpoint. Disenchanted by the circus at United, and apparently unsuited to the latest attempt at a solution, a fresh start is probably the best way forward. Finding a club willing to take on at least the bulk of his hefty salary, though, will be difficult

and, as Sterling’s drift since leaving City demonstrates, form, once lost, is not so easily regained.

View image in fullscreen