This is a big game and unarguably the biggest game of the midweek round of matches in the English Premier League. Arsenal will travel to Old Trafford to take on Manchester United in a ground they have not won since Emmanuel Adebayor scored the winner in September 2006 at Old Trafford.
The gunners still remain unbeaten since their losses to Manchester City and Chelsea at the start of the season and are coming on the back of a morale-boosting derby win over arch-rivals Tottenham Hotspur on Sunday.
On the other hand, Manchester United are struggling for consistency in the league. They drew against Southampton 2-2 over the weekend in a game where they were 2-0 down.
Here are four things that could swing the tie in either of the teams' favour.
#1 The pace of Rashford and Martial
In times past, the duo of Rashford and Martial have been a thorn in the flesh of the gunners with their pace and trickery. Anthony Martial is a trickery winger and has the capability to turn up with goals when it matters most as seen already this season.
Marcus Rashford will test the likes of Sokratis and Mustafi with his pace. Paul Pogba has the ability to pick the runs of Rashford, especially against an Arsenal backline who plays with a high line, to keep their opponent at bay. The Arsenal defence will have to be wary of the pace of both players if they hope to come up with anything from Old Trafford.
Jose Mourinho emphasis on wing play highlight why this is important. Hector Bellerin against Martial promises to be an interesting contest. The Frenchman's trickery and pace will be up against Bellerin who has pace as well, but his ability to deal with Martial's trickery could be key to unlocking The Gunners' rearguard
Rashford will likely be on the heels of Sokratis and Mustafi to beat them for pace as well as beating the offside trap, if he succeeds, it could turn the game in United's favour.
#2 Arsenal's incisive passing and directness may also prove to be key
Unai Emery has added two things that Arsenal were lacking under former manager Arsene Wenger: Forward incisive passing and directness. The team under Wenger were always known to be dominant in ball possession but for all the possession, they could go the whole first half without registering a shot on target.
This was usually due to the Frenchman's overemphasis on "tiki-taka" football. It became quite easy for opposing teams to beat the Gunners.
All they did was sit back and wait for their moments to counter-attack. Under Emery, it must be said that the team are more incisive with their passing games and most notably, positive when attacking the opposition. If Arsenal get their passing game on, United will struggle to cope with them.
This could wear them out as the game progresses and leave holes in the defence for the Gunners to exploit.
Arsenal has always come unstuck against United at Old Trafford, because of their insistence of scoring the "perfect" goal and playing attractive especially after the Invincibles' era
Using the likes of Alex Iwobi to run at the United defence as well as Pierre Emerick Aubameyang's pace in behind the defence could also catch the United backline off guard, especially one under Mourinho, who are not particularly good at finishing games well when they are wearied out.
#3 Arsenal have to be stronger when defending from set pieces
Manchester United will definitely be a threat from set-piece situations with the likes of Fellaini, Pogba and Matic. Granit Xhaka will miss the United game as a result of receiving his fifth booking of the season against Tottenham on Sunday. The Gunners will have to devise a plan to stop the threat the players United have in these situations.
Rob Holding seems to be the tallest of Arsenal's centre-backs and may have to stay with Fellaini when defending set plays. If the Gunners unnecessarily give fouls away close to their 18-yard box, United could hurt them.
Lucas Torreira is not the tallest of players, so it remains to be seen who partners him in midfield that is capable of defending from set pieces comfortably.
They will also need to be disciplined not to give fouls away in dangerous positions where United can take advantage of.
Arsenal will have to be a lot stronger defending from set plays with an eye for Fellaini.
#4 The 3-4-3 formation for Arsenal is a no-brainer
Arsenal looks more secured in recent games playing with three centre-backs and giving the likes of Bellerin and Kolasinac more room to cause damage upfront and also give them balance while defending.
A four-man defence may actually not be a good idea especially against a United team who will still be looking to use the pace of Rashford and Martial to cause damage on the counter.
The fullbacks often join the team in attack, leaving only two centre-backs to deal with counter-attacking situations in the game.
The 3-4-3 formation will also give room for Alexandre Lacazette and Aubameyang to cause problems for United, with the kind of pressing game Emery has imbued in his team.
United are not particularly good passers of the ball from the back and will look to go long, but when they try to do that the two in-form Arsenal strikers will be looking to pounce.
It remains to be seen whether Lacazette starts alongside Aubameyang, but one thing is sure: both of them will have to play together sometime in the game to unsettle then United defence.