Things can turn quickly in Scottish football.

The second act of this season’s Old Firm show on Sunday is still a hard one to call, partly because it’s at Celtic Park and also because there surely has to be some kind of response from O’Neill’s team to their pitiful fate at Ibrox last weekend.

Their fans will be worried, though. Five goals given up against LASK, a desperate experience at Ibrox – and now this.

In moments on Thursday, some of their football was reminiscent of darker days – the failures of Cluj and Copenhagen in 2019 and 2020, when Bayo and Bolingoli were in the building; Sparta Prague in 2020, when Klimala and Ajeti, Duffy and Laxalt were in the team.

It was all very Legia Warsaw, very Salzburg, very Maribor. The energy levels were low, the booing was loud and the feeling of a side with no answers was unmissable.

In the aftermath, O’Neill spoke about frustration, failure and psychological damage, how low moments like these hit you hard and test your resolve. He promised to “get ourselves together” for Rangers on Sunday but his tone was flat and a touch tired.

He outlined some of the ways in which Celtic were deficient on the night but didn’t talk with the spirit of a man who had answers. In many ways his post-match comments mirrored his team’s performance – leaden, stale, disheartening.

O’Neill has fixed many problems over the years, not just in his first trophy-laden spell but in his return to chaos last season. He restored order and confidence, two things that have been lost.

The force of his personality gave Celtic fight. They were not always pretty to watch but they were ferociously hard to beat. Nobody managed it on the title run-in.

That kind of never-say-die only seems like yesterday, but in other ways it feels like an awfully long time ago.