After his hat-trick against Bournemouth and, again, after his Champions League match-winner against Napoli, Salah opted for the stiff, inscrutable, stony-faced pose, a puzzling anomaly made all the more striking as he was being mobbed and buffeted by gurning, hysterical teammates.

No matter that, unlike Salah, most of Gary Lineker’s goals seemed to be scored from inside the six-yard box: here was a serial marksman who used to celebrate every one of them as if he’d just clinched the World Cup for England with an overhead kick in the last minute of time added on.

And proper order too.

So no surprise then that, as host of BT Sports’ coverage of that Champions League win, Lineker deemed Salah’s non-celebration sufficiently newsworthy to warrant canvassing the opinion of one of his guests, Luis Garcia.

“I think he’s not feeling the same as he did last year,” offered the former Liverpool striker. “Last year everything was coming easy and this year he’s struggling in a few of the games, having chances and not scoring. Probably he’s trying to prove himself and well, tonight, once again, he done it.”

Indeed. Just for the record it might be worth noting that, after a slowish start which had some folk raising the spectre of second-season syndrome, Salah has now registered a very far from shabby 13 goals in 22 appearances this term.

And his winner against Napoli was a classic of the ‘if at first you don’t succeed...’ kind. Napoli’s formidable defender Kalidou Koulibaly, reportedly a Man United target — but then, who isn’t? — had proved an almost impenetrable barrier for Salah for half an hour of the game. And on the one occasion when the latter did find himself with a clear sight of goal, an uncharacteristically heavy touch had proved his undoing. But in the 34th minute, with Koulibaly still trying to do the right thing by showing him down the right-hand side, Salah improvised brilliantly to ghost past his marker and, after giving goalkeeper David Ospina the eyes, squeeze his shot home at the near post. In tight situations like that, few players are as nimble-footed as Salah, whose quick thinking and economy of movement is a lethal combination.

And yet, still no celebration. But whatever it is that has wiped the smile off Salah’s face, it’s the kind of thing that Liverpool’s opponents at Anfield tomorrow could only possibly regard as a luxury problem.

While Anfield was rocking on another big European night this week, Manchester United were spurning the chance to top their own Champions League group with a shockingly inept performance in Valencia. Jose Mourinho suggested yesterday that his team are far from being one that is built in his own image, which would be a reasonable thing to say if he was talking about himself back in, say, his Chelsea prime. In truth, the grim reality is that this Man United are a virtual doppleganger of Mourinho 2018: gloomy, repetitive, defensive, and increasingly painful to watch.

It’s not that United are lacking in quality players or even phases in games when it all suddenly clicks and they look, if not world-beaters, then at least like a side which should no way be 16 points behind Liverpool in the Premier League and maybe even still have enough about it to confound a few expectations in Europe next year.

But those good days at the office always feel improvised and temporary, hastily assembled rather than built on solid foundations. There is no underlying cohesion, no convincing evidence of collective purpose and absolutely no sense that players and manager are working off an agreed plan or to a shared vision. Apart from somehow getting through the next 90 minutes. Frankly, it’s all gone a bit Brexit at Old Trafford, with any victory gained against the head feeling more like a stay of execution than the basis for a credible, long-lasting solution.

Jamie Carragher believes that a victory for Liverpool — which, remarkably, would be the first over their great rivals since 2014 — would see Jurgen Klopp’s team “laying down a marker” as serious title contenders.

But that sounds like an interpretation which, in the context of this latest meeting of the old foes, owes more to the fixture’s traditional reputation than the reality of the balance of power in 2018. These days, from their new-found solidity at the back, through a hard-working if not overly inventive midfield, to their thrilling attacking trident, Liverpool are superior to United in almost every department. (And even between the posts, as he showed against Napoli, Allison is closing the gap on De Gea).

Which isn’t to say, of course, that Liverpool are guaranteed victory tomorrow. But even if, in going to Anfield as Premier League also rans before most of us have put up the Christmas tree, United find enough incentive and professional pride to raise their game and, as a certain former gaffer once put it, knock Liverpool “off their f**king perch”, the only real significance of the result would lie in the dent to their opponents’ title ambitions.

For Manchester United, it would likely be just another dead cat bounce, a reason to smile, certainly, but one that, by now, the long suffering faithful would expect to have just as quickly wiped off their face.

It’s the Old Trafford way these days: things only get better before they get worse.

And if Liverpool go about it in the right way tomorrow, even that meagre consolation should be denied the visitors.