Ibrox will stage a game between second and third in the Scottish Premiership. Given that Hearts are proving so impossibly stubborn at the top of the Scottish Premiership, refusing, it seems, to do what is expected of them by the old order and kindly going away, the pressure returns to Rangers and Celtic in Sunday's must-win to end all must-wins.

Martin O'Neill turns 74 on the day. What better way to spend it than in the furnace of the Old Firm? Candles on the cake won't concern him. Points on the board will be the only thing on his mind. A draw is of little use to either club now. This game demands a winner and if there is a winner there has to be a loser. Heaven help them. The wrath will descend, especially if it's Celtic, you suspect. It's not like Rangers folk will shrug in defeat - it's not exactly their style - but Celtic fans are an angrier and more frustrated crew right now.

Andrew Cavenagh, the Rangers owner, got rid of a manager, a chief executive and a sporting director, as the fans hoped he would, and then spent millions on players in the January window on top of the millions he spent in the summer. They have a popular manager in Danny Rohl and what looks like ambition in the boardroom. In the grand scheme of things, Rangers fans don't have a huge amount to complain about. Their Celtic counterparts are in a different place. Most are apoplectic with their board and split on the way to voice that anger.

In the underworld of social media, they are now arguing among themselves. Accusatory language is flying. Toxicity is pervasive; draining and self-defeating, but almost unavoidable. The Celtic Way is all of those things at the moment. Both of these clubs have been soap operas all season. Rangers have an awful lot of work to do, but they are at least pointing in the right direction. With a manager to find and with the same unpopular people who appointed Wilfried Nancy in charge of finding him, Celtic look directionless.

What plan can they have in the badly needed rebuilding of a team when there is no manager there to rebuild it? These clubs have experienced existential crises and that, on its own, is compelling to witness. Rangers had a "£20m net spend" in the summer and went again in January in a major way. They're still behind Derek McInnes' Hearts. When the Old Firm look over their shoulder they can also see the coming force that is Motherwell; winning and entertaining and almost incapable of conceding a goal in the league under the brilliant management of Jens Berthel Askou.

In the past decade in Europe, Celtic have made an estimated £195m in prize money and television rights. They have sold three different players for £25m apiece, another five for between £10-£20m and a bunch of others in the £5m-£10m bracket. Significant profit has been made. They have £67m in cash reserves. Rangers have made close to £100m from European football in those 10 years. Hearts have earned about a tenth of that and Motherwell have made about a tenth of what Hearts have made.

And yet the way of things at the top is under massive threat - and it's intoxicating. It's always tense when the Glasgow giants meet, but this one will have a slightly different vibe. There's jeopardy for both of them, not just from each other but from Hearts and Motherwell, too. The Old Firm are playing catch-up while being hounded from below. It's unique in the lifetime of many, many people who are watching.

And there's been some verbal jousting in the preamble to Sunday. Luke McCowan, buoyed by a goal and a win against Stuttgart on Thursday night, gave it the big one about Celtic being the best team in the country, despite significant evidence suggesting they are not. "We know that if we're at it, no team in the league touches us," said McCowan the other night. He backs his team. Fair enough, but… Celtic, as if anybody doesn't already know, are sitting third in the Premiership.

If it wasn't for their ability to score late winners - 87th and 90th minute in two games against St Mirren, 90th minute and 90th minute in two against Kilmarnock, 90th minute against Motherwell - then their title hopes would have already turned to dust. Credit to them for having the bottle to win those games, but they were all desperate grinds. As were others they scraped home in. O'Neill has dragged them forward by the scruff of the neck, but it has all looked very tired, very stressful, very on the edge of blowing up.

He is still without some mainstays in defence - Cameron Carter-Vickers and Alistair Johnston. Auston Trusty is suspended. They've dropped points in 10 of their 27 games. The majority can be pinned on the ludicrously ill-judged appointment of Nancy, but under Brendan Rodgers they lost to Dundee and Hearts and under O'Neill lost to Hibs and drew with Hearts. A controversial red card in both of those games, of course, but the performances were still a mile off what Celtic used to be.

Compared to this point last season they've won five fewer games in the league and have lost five more games, they're -28 on goals scored and +9 on goals conceded. They're 15 points worse off. A year ago they were sitting pretty at the top, 13 points clear. They'd just taken Bayern Munich to the wire in the Champions League. Life was good.

Rangers are down three in terms of points and wins, but have lost three fewer games, have nine more goals, with only one more conceded this season than at this stage last season. With such a hideous start to the campaign, getting back in the hunt must feel like the second chance they thought they'd never have.

McCowan's words sparked something - and it was good knockabout stuff. Rohl reminded people on Friday that Celtic have lost seven games to Rangers' two. He also riffed on why Celtic didn't push for more goals against Stuttgart on Thursday and speculated on who O'Neill might pick in goal on Sunday - Viljami Sinisalo, who did well in Germany, or the increasingly error-prone veteran, Kasper Schmeichel.

When talking about another manager's players, Rohl knew what he was doing - and O'Neill didn't like it. "It's quite extraordinary, an extraordinary comment to make, really," said O'Neill of Rohl's view on Celtic supposedly not going for it against Stuttgart." He also called Rohl "a very young man", which was tantamount to telling him to "sit down, you know nothing of this fixture". He said Rohl was behaving like a fan.

"I'm glad he's really interested in the make-up of my team, you know. He hasn't been in Glasgow that long, has he?" Long enough to know what's at stake. And, possibly, long enough to know how to get under the skin of an old master. Talk is cheap, though. Talk wins you nothing. And how both of these clubs need a win at Ibrox. It's an Old Firm derby, but not as we've known it for an awfully long time.