Arsenal managed to out Arsenal themselves on Thursday night at home to Olympiacos.
They had looked to have turned a corner in 2020 and were making genuine strides towards salvaging an absolute disaster of a season before capitulating in front of their own fans last week.
To lose in the manner they did will be particularly painful.
They looked set to ease through after going to Greece and claiming a 1-0 win and then looked to have spared their blushes when Pierre Emeric Aubameyang spectacularly volleyed home in extra time, only to concede almost straight away and for Aubameyang to miss a gilt-edged chance to save them again.
With their European hopes extinguished and their hopes of finishing in the top four hanging by a thread, a defeat at Fratton Park on Monday night would all but end their season.
Arsenal’s season literally depends on them putting a good cup run together and they will be going all out to prevent any further upsets.
Portsmouth, meanwhile, find themselves in the midst of a much more important battle to secure promotion to the Championship.
They don’t need the distraction of the FA Cup as their season reaches a fever pitch and, besides, they already have the Football League Trophy final to look forward to.
Having said that, Arsenal can never be relied upon to be defensively solid and Portsmouth have been in a rich vain of goalscoring form, scoring 11 in their last five games.
Arsenal may need to score twice if they are to snatch victory.
Mikel Arteta is likely to give either Gabriel Martinelli or Eddie Nketiah a run out on Monday, or both.
Martinelli has slowed down somewhat after an explosive start to his Arsenal career and he has failed to kick on after his wonder goal rescued a point for the Gunners in Stamford Bridge in January.
However, Martinelli initially made a name for himself in games like this, netting twice against Nottingham Forest in the League Cup before repeating the trick against Liverpool’s reserves in the following round.
He also scored in home Europa League wins against Standard Liege and Vitoria and he seems to particularly thrive against supposed weaker opposition.
If he gets a start on Monday night, he should get plenty of chances to end his four-game scoring duck.
Despite playing well in recent weeks, Arsenal have struggled to break teams down regularly.
They have gone in level at half time in each of their last five games and seem to come to life in the second half, considering they won three of those games.
Playing away from home against lower league opposition on what will be a cold and possibly stormy Monday night, they are certain to face early pressure from their hosts.
It may take time for Arsenal’s players to adjust, especially given they are just off the back of a chastening defeat.
When they faced Leeds in the third round – the last time they faced lower league opposition – they faced similar problems in the opening half and only really got to grips with their opponents in the second half.
It might be a sixth game in a row where they go in level at the break.
*All odds correct at time of publication