That’s the million-dollar question for Unai Emery on Friday night, isn’t it?
How do you throw a spanner into the works of a machine that is well-oiled and chugging along nicely, showing no fear and having recaptured a little of its Ferguson-ian lustre?
I think the fans will have a big part to play in making this fourth round FA Cup clash as uncomfortable as possible for the visitors, much as they did in the north London derby.
If ever a 12th man were needed, it is in a game that genuinely feels like it could be a memorable one, a little throwback to the early 2000s, when the Premier League’s two giants slugged it out, showing no quarter and getting none in return.
But for every scream, shout and curse from the stands it will need twice as much input from the players, who must be prepared to run themselves ragged.
Getting the selection right will be crucial to that end. The setup against Chelsea was a good one and may well serve as the blueprint for the visit of United.
But Emery will need to be mindful that United have an effective 4-4-2 diamond of their own that will need to be nullified. Perhaps putting Aaron Ramsey on Paul Pogba might prove as effective as it did against Jorginho, or perhaps Ole Gunnar-Solskjaer is wilier than the rigid Mauricio Sarri.
The only thing that’s certain is that Emery will need a new right back to replace the injured Hector Bellerin and who he picks will make a difference. The consensus seems to be that Ainsley Maitland-Niles will be the man given the nod but, in a game where iron concentration is needed for 90 minutes, perhaps Stephan Lichsteiner would be the wiser option.
It may well lessen our attacking options on that side but the Swiss has experience of the biggest games on the biggest stages and you can be sure he will thrive under the Friday night lights.
While obvious signs of weakness have been fleeting since the departure of Jose Mourinho, United’s victory over Tottenham showed that while their attacking abilities have been rejuvenated, their defence remains naive and vulnerable.
If truth be told, Tottenham should have scored half-a-dozen goals but were thwarted by a combination of excellent goalkeeping and shambolic finishing.
If United defend in the same sort of fashion at the Emirates, you’d fancy us to score a couple at least.
As the manager said in his pre-match press conference (hyperlink), however, it’s going to need a whole team defensive effort, of the sort we saw against Chelsea, if Arsenal are to stop the goals flooding in at the other end.
We’re going to need Alexandre Lacazette and Pierre-Emerik Aubameyang to track back on occasion, as they did last week, while Matteo Guendouzi and Lucas Torriera are going to have to work the central and wide areas furiously, running themselves into oblivion.
At the back, Laurent Koscielney and Sokratis are going to need all the shit-housery they can muster against the pace of Marcus Rashford and Jesse Lingaard. Their positioning and line will need to be perfect and they will need to be every bit as hostile as they were with Eden Hazard and co.
In short, Arsenal will need to be in top gear and functioning at their maximum if they want to get past a team that is brimming with confidence at the moment.
The fixture at Old Trafford a month or so ago will have little bearing on this one.
Matches against Liverpool, Tottenham, and Chelsea have shown a big-match appetite among both Arsenal fans and players so far this season and I hope the sort of relentless, aggressive performances we saw in those matches can be repeated on Friday.
Victory will not only book our passage through to the next round of the cup, it might also serve to show the rest of the league that, below the surface at least, weaknesses remain in this United lineup that can and should be exploited.