Look at the facts of their performances on paper. In the Premier League they are averaging over two goals a game (39 in 18), have defeated Arsenal and Tottenham while drawing at Liverpool, and have the joint-best defensive record, having conceded only 12 goals. What more, Mourinho may think, may people want? His problem, of course, is that Manchester City are hovering above them with all the subtlety of a solar eclipse.

In Mourinho's defence, Pep Guardiola's team are putting together a sequence of form the like of which English football has never seen, and it is not clear how sustainable this is. If City falter, Mourinho can argue his team will be there to swoop.

Yet this is also a case against Mourinho. Like Guardiola, he has abundant resources at his disposal. Unlike Guardiola, many of his players are regressing sharply. Ander Herrera has been constrained so severely by his last two managers that he seems to find great difficulty in acting as a midfield orchestrator. Henrikh Mkhitaryan now looks likely to leave after falling out with Mourinho over his defensive duties. It is worth noting that Antonio Conte's liberation of Eden Hazard from those same defensive duties, imposed under Mourinho, is a key reason why Chelsea won the Premier League in Conte's first season.

It is well documented that two of the league's brightest attacking talents, Kevin De Bruyne and Mohamed Salah, were discarded early in their careers by Mourinho. If the United boss is being criticised for his attack, then he can seek solace in his defence. Yet here, despite the excellence of that record, there is room for significant improvement. As was the case under Louis van Gaal, a key reason for United's strength at the back is the often otherworldly brilliance of David De Gea.

The problem with Chris Smalling and Phil Jones, to name just two, is that beyond their inconsistency -- less so in Jones' case this season -- they are not particularly good at building the play from the back, allowing teams to set their defences before United come at them. This therefore helps to neuter United's rapid counter attack.

Gary Neville recently expressed frustration at the uneven recruitment at Old Trafford, stating that since the departure of Sir Alex Ferguson the signings at United had often been poor. That is a slightly revisionist view of events, given that Ferguson toward the end of his career did not renew the midfield in particular as well as he once had. Yet Neville's critique is largely valid and widely supported. The problem is that the gap between the best player in United's squad and their worst is vast. Meanwhile, Manchester City can afford to play superbly and leave Bernardo Silva -- a player who could start for any team in world football -- on the bench.

It is reductive to say that Mourinho should simply throw money at the problem. Yet there is significant work to be done when it comes to the quality of his playing staff, and until that work is done United will remain frustratingly out of European football's elite tier. In retrospect, Mourinho's strategy of bringing in four players each summer was insufficiently ambitious. The pedigree of those players is not in dispute -- even though Eric Bailly is worryingly prone to injury -- but far more exhaustive surgery was needed.

In some respects, the bloody nose Guardiola received in his first Premier League season was the making of him. He stepped back and reassessed the rot, and he has addressed it in spectacular style. Mourinho seems to be due a similar learning curve -- he is seeing, as other managers in the Premier League have long seen, that a reactive, risk-averse strategy is not enough to be decisive in the season's key matches. It is worth noting, too, that those "key matches" are not necessarily those against United's direct rivals -- they are the contests against teams like Huddersfield Town away, where the wealthier teams have more of a burden on them to impose themselves.

There is an argument that, under Mourinho, United may never consistently emerge from third gear. They will continue to provide devastating performances against teams who open up against them, but will otherwise remain unable to impose themselves when it truly counts.

These might sound like harsh judgements, but the margins between success and failure at the top level of club football are vanishingly small -- and, for the time being, Mourinho finds himself on the wrong side of the arm-wrestle.