Despite going into the tie off the back of a good 3-0 Europa League win at home to Dundalk, the Gunners have lost three of their last four in the league and face a very tough task in their trip to United.
Here's the side Mikel Arteta should select for Sunday's clash.
1. Goalkeeper & Defenders
Bernd Leno (GK) - After Leno’s blunder in the Europa League last week, Rúnar Alex Rúnarsson was given his debut in the competition on Thursday night, keeping a clean sheet in the process. However, Leno has become a trusted member of Arteta’s squad and he should start this one.
Hector Bellerin (RB) - Without a doubt Arteta's number one right back and he’s good value for it after some tidy performances domestically and on the continent. One of his better starts to a season for Arsenal.
Shkodran Mustafi (CB) - With David Luiz out injured, Mustafi is likely to start for just the third time this season after helping the Gunners to a clean sheet at Dundalk in midweek. The German has some boots to fill after a decent run of performances from the Brazilian centre-back pairing.
Gabriel Magalhaes (CB) - The summer arrival has settled well into the Premier League so far and is showing a dominance at the back that Arsenal have previously lacked. The impressive young Brazilian will be hoping to thwart an in form Marcus Rashford.
Kieran Tierney (LB) - Another first choice full back under Arteta and probably one of the first names on fan team sheets. No doubt that Tierney will start and build on a promising start to the campaign.
Thomas Partey (CM) - Arsenal’s signing of the season. Showcased his ability in Europe and will be a familiar face in the heart of the Gunners’ midfield for some time to come. Will be key to disrupting United’s play.
Granit Xhaka (CM) - Another Arsenal player whose form has been revived since the arrival of Arteta. So close to being the forgotten man last season, Xhaka has started almost every game so far. His partnership with Partey in midfield will be essential in allowing the four creative players to get forward.
Dani Ceballos (AM) - Back for another loan spell at Arsenal, Ceballos is yet to set the Emirates alight. Already up to ten games in all competitions, the Real Madrid loanee is clearly player liked by Arteta. A strong performance at Old Trafford could kick-start his campaign.
Bukayo Saka (LW) - The youngster has provided the likes of Pepe and Willian with some real competition out wide, but could, likewise to his peers, do with chipping in with a few more goals. Saka's versatility has been utilised plenty of times already by Arteta and he's expected to start ahead of Lacazette.
Pierre-Emerick Aubameyang (ST) - Willian’s reintroduction could see Arteta drop Lacazette and move Aubameyang into the central role. Still with only one Premier League strike to his name this season, the pressure is mounting on the striker to help end Arsenal’s run of two league games without a goal.
Willian (RW) - The return of the Brazilian will be a huge boost for north-Londoners. Tireless, creative and intelligent, Willian adds a much needed energy to an Arsenal side who will be desperate for a Premier League goal.