Disquieting news conferences are nothing new with Jose Mourinho. Even during his heyday with Porto, Chelsea and Inter, they were usually cold, beguiling encounters, a glance into the war room of a calculating general.

But where once there was intrigue, now there is bitterness and boredom. Mourinho's latest 20-minute diatribe in the United States came after weeks of frustration, in which he rattled off barbs at Liverpool, Anthony Martial, Paul Pogba, Antonio Valencia, young players and the transfer window, like some vitriolic Gatling gun with a stuck trigger.

You might have noticed the military theme by now. That's because Mourinho and Manchester United are gearing up for a fight: a fight to stay relevant in a modern gung-ho game as their rivals threaten to vanish over the horizon. And it seems Mourinho knows it.

Of course, this is Mourinho's 'Dreaded Third Season' at United, the time at which his apparent revenge mission on the world takes its toll – at least, if you ignore his third terms at Porto and Inter, when he became a hero by winning the Champions League. But if there are any fears about him bringing down the walls around him this year, it's only because he has spent the last 12 months chipping away at the foundations.

It seems remarkable that only a year has passed since he said he had "never worked with a group I like as much" as his United squad. Since then, his public sniping at his players has sounded like a game of Excuses Bingo: Luke Shaw, Pogba, Luke Shaw, Martial, Marcus Rashford and Luke Shaw again have all been brought up when deflective tactics were needed. Even Valencia, expected to succeed Michael Carrick as permanent club captain, had his recent injury blamed on him taking too much holiday.

"This is not my squad," Mourinho protested after United's 4-1 International Champions Cup loss to Liverpool. Sometimes it's difficult to know who is, or who even wants to be.

That's the other problem with modern Mourinho: his pulling power has waned. Even just two years ago, it was enough to tempt the best players from Italy, France and Germany to join a United side with no Champions League football, although Ed Woodward's dip into the club's coffers no doubt helped persuade Paul Pogba, Zlatan Ibrahimovic and Henrikh Mkhitaryan to join.

The latter two have left, Pogba has had a rare taste of life on the bench, and it's hard to see where the next marquee arrivals will come from. Mourinho has been very clear about wanting two new players but, despite his continually strong track record on United's commercial front line, Woodward has looked unable to deliver beyond the deals for Fred, Diogo Dalot and Lee Grant.

The Gareth Bale rumours stopped surprisingly quickly this time, and speculation of a bid for Mateo Kovacic, set to join Chelsea on loan, was met by claims the midfielder does not fancy playing the Mourinho way. It means United head into Friday's Premier League opener against Leicester City with no upgrades on converted 30-something wingers as full-backs, nothing to bolster central defence or the wide attacking positions, and the likelihood that Matteo Darmian and Anthony Martial will have to start despite wanting to leave.

The concerns are magnified by the way their rivals have strengthened. Manchester City added Riyad Mahrez to a record-breaking side that finished 19 points above United, while Chelsea jettisoned the tired Antonio Conte to bring in bold, brash Maurizio Sarri and Jorginho, the midfielder who embodies his style. Arsenal finally look like a team with a plan under Unai Emery, having accepted Emirates Stadium would not collapse into rubble if Arsene Wenger were removed. And while Jurgen Klopp might have abandoned his principles by spending close to £200m in this window, he has strengthened every one of the weak points of a team that played a Champions League final three months ago. Well, at least that brought a smile from Mourinho.

United still have time to buy and are not bereft of quality – let's not forget that last term's haul of 81 points was the most they have managed in the Premier League since Alex Ferguson bowed out.

And yet, that feels like part of the problem: Mourinho's United are doing just enough, taking baby-steps back towards the summit. An EFL Cup, a Europa League and a second-place finish over two years might ward off the sack, but it should not feel adequate for this club, or this manager. It never used to.

The fear is now that, unless Mourinho abandons his grouching and rallies his troops to his cause, 2018-19 will be another season where he and United are talked of in terms of what they were, and how long ago those glory days seem to be.