It could be the second successive seismic Sunday for Arsenal, ending the world as they have known it for two decades. Last week brought confirmation that they would finish below Tottenham in the Premier League for the first time since 1995. This could render it almost certain they will finish outside the top four for the first time since 1996.
Even defeat would not make it a mathematical certainty. Anything short of victory would make it hugely probable. And yet an Arsenal win might carry similar consequences for Manchester United.
Should the Red Devils' six-month unbeaten run in the Premier League end where it started, in London, their attentions will have to be concentrated on the Europa League if they are to qualify for the Champions League. This has the feel of an eliminator, a game to thin out the list of contenders.
It highlights the way this rivalry has changed. For years Arsenal and United seemed to be the top two. Now they sit sixth and fifth respectively and Arsene Wenger's side could kick off in seventh.
A season that has brought ever greater indignities for Wenger still offers the opportunity to embarrass an old enemy. Given the insults Jose Mourinho has directed at the Frenchman over the years, Wenger could be forgiven for taking some satisfaction if he dents the Portuguese manager's top-four push.
That could entail a historic achievement. Thirteen years after they first met, Wenger still has not won a league game against Mourinho. But the Portuguese, who has yet to see his United score away from home at top-six opponents, could ease Wenger's passage to victory.
He will make changes to focus on the Europa League semi-final against Celta Vigo. Saying so may be an opportunity to get his excuses in early or a way of camouflaging his true intentions.
It is worth remembering he named a seemingly lesser side against Chelsea last month and still beat them. His history shows depleted teams can triumph and that he is dangerous when underestimated.
Whichever, this is a game that may be determined less by strengths than weaknesses. The fatigue of an injury-hit United group could cost them, but that may require Arsenal to show more intensity, urgency and quality than they have demonstrated in recent weeks, the FA Cup semi-final being the exception.
The Gunners' defensive frailties could be exposed, but United will have to demonstrate more attacking impetus; the chances are that Mourinho will look to use pace on the break as a weapon.
There will be the usual focus on Arsenal's mentality, especially that of Mesut Ozil, in a familiar test of United's collective powers of resilience and resolve. It will be intriguing if Wenger sticks with his 3-4-2-1 and instructive if Mourinho dissects it.
Because while the prize of victory has been bigger in previous games between these sides, the cost of defeat rarely will be.
ARSENAL V MANCHESTER UNITED
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