In the moments which followed Mika Baur sweeping the ball into Celta Vigo’s net early in the second half, there was joy around Celtic Park. But you felt something was missing.

There was a lack of belief that the first goal of the night would be the last, a lack of trust in Martin O’Neill’s side to shut up shop and seal the three points.

Football supporters tend to be optimistic by nature yet they are not blinded to reality either. This Celtic side lost five goals away to LASK, three at home to Ferencvaros and four away to Benfica. They can look decent going forward yet they are routinely awful when asked to defend at that level.

You had to suspend reality to believe that a slick and accomplished Celta Vigo side would not score in the 43 minutes that remained.

The minute Javi Rodriguez netted one, the only question was when Celta would strike again. Three minutes was the answer, the defender the hero again for the visitors. Like the old Glasgow buses, Celtic concessions rarely come alone these days.

There was a feeling of acceptance among the home supporters that the game was up the instant the Spaniards got their noses in front. When you have seen so many similar stories unfold in recent times, it becomes harder to envisage an alternative ending.

Celta’s trip to Glasgow had evoked memories of how it used to be in these parts. Nearly 24 years ago, they had no response when Henrik Larsson netted in the first leg of the UEFA Cup tie.

In that run to the final, O’Neill’s side would claim the scalps of Blackburn, Liverpool and Stuttgart.

Around that time, Juventus, Lyon and Barcelona all left Parkhead defeated. After Gordon Strachan took charge, the names of Manchester United, Benfica, AC Milan and Shakhtar Donetsk were added to the list of the vanquished.

For a spell, Celtic Park was as tough a venue as there was in European football, the thunderous noise simultaneously inspiring the home side and spooking the opposition. It was truly a sight to behold.

For that dynamic to exist, though, supporters must have something to believe in. And, right now, the evidence of their own eyes offers very little by way of encouragement.

By time up on Thursday, you couldn’t help but compare and contrast the picture inside the ground to that of almost two years ago.

Under Brendan Rodgers, Celtic’s last Champions League campaign started with a 5-1 thumping of Slovan Bratislava.

After a chastening night in Dortmund, Celtic responded with a commendable draw away to Europa League holders Atalanta.

By common consent, the display Rodgers’ side produced in the 3-1 slaying of RB Leipzig on November 5 was the most complete in Europe’s premier competition in a generation.

With Celtic accruing enough points from Club Brugge, Dinamo Zagreb and Young Boys to progress, their prize was a shot at Bayern Munich.

While Rodgers’ men were ultimately eliminated by the Bavarians, their display in the Allianz was outstanding. It felt like a standard had been set which would see Celtic as regulars in the play-off round of the top-tier tournament, perhaps occasionally venturing further.

The demise to this point has been nothing short of staggering.

In their next outing, Celtic couldn’t score a goal in 210 minutes against Kairat Almaty as their Champions League ambitions for last season were ended.

They were picked apart by Braga, Midtjylland, Roma and Stuttgart in the Europa League.

Since beating LASK at home in this year’s Champions League play-off, they’ve lost to the Austrians, Ferencvaros, Benfica and now Celta Vigo.

There was a time when Celtic could land a blow on the heavyweights of the European game. These days, they’re a punchbag for second and third-rate sides.

Anyone employed by the club who isn’t mortified by the current state of affairs certainly should be.

In the 36-team Europa League group, O’Neill’s side presently sit in 35th place. Only Ararat-Armenia, a club whose stadium capacity is listed as 1,428, sit beneath them. They are plankton in football’s ocean and they now have Celtic for company.

Sure, there are five games to go, 15 points to play for. But where is the form line to suggest that this Celtic team can stage the mother of all comebacks against the likes of Besiktas and Marseille?

It scarcely requires a deep insight to establish how such a desperate position has been arrived at so quickly.

Celtic’s predilection to selling its prized assets remains as strong as ever. From the team which performed so admirably in Munich, Nicolas Kuhn, Arne Engels and Daizen Maeda were flogged for big money. Kyogo Furuhashi had already been transferred.

Subsequent transfer windows saw a continuation of the hollowing out of the squad. Camilo Duran and Mika Baur have been fine acquisitions but the general quality has been diluted.

The goalkeeping situation is just one case in point. Celtic had a year’s notice that Kasper Schmeichel’s time was up in the summer.

Having refused to pay Blackburn £4million for Balazs Toth in January, they brought in Sam Johnstone on loan from Wolves on transfer deadline day.

Neither the Englishman nor Viljami Sinisalo have convinced. The same could be said of the majority of Celtic’s signings for long enough now.

On Wednesday, Shaun Maloney attributed the contrast between Celtic’s league and European results to the structure of the side rather than the individuals within it. In fairness, the club’s assistant manager could hardly claim anything else.

Few observers, though, put Celtic’s current travails in Europe down to a particular system and the players learning it as they go. It’s down to the dearth of quality both in the starting line-up and the bench.

Too many players who do a job domestically but who are routinely exposed when asked to step up a level. Chris Sutton recently labelled the team ‘flat-track bullies’ and you knew exactly where he was coming from.

You would not bet against Celtic winning the title again this season. They’ve done so in 14 out of the past 15 campaigns, after all. But domestic success no longer camouflages the wider picture of a club moving ever closer to being an irrelevance in Europe.

The absence of the Green Brigade on Thursday was the latest development in the ongoing feud between the club’s hierarchy and various disaffected supporters groups.

While those who opted to forgo their usual spot and watch the game from afar will have taken no pleasure from the outcome, another European defeat to add to the ledger only served to underscore their point.

As a football club, Celtic has a history and a support which is the envy of most in the world.

Right now, though, at boardroom level, it badly lacks vision, strategy, ambition and humility. It requires modernising from top to bottom. It needs leadership and people taking responsibility when all it has is stuffed shirts and occasional rambling statements from a minority shareholder on the official website.

A football team on the park is always reflective of the functionality of those above them. It’s little wonder O’Neill’s outfit aren’t up to the job.