I wrote on Tuesday of how United's success in the games early stages owed much to Ferguson's decision to play a 4-4-1-1 with Valencia operating wide as a classic right winger. Chelsea's outside backs like to get forward and join in the attack. When they lose possession Ashley Cole and Branislav Ivanovic are often high up the pitch, leaving them vulnerable to counters down the flanks. It was Rooney rather than Valencia who had drifted to the right to spring the counter on United's first goal but it resulted because Cole had gone forward to join in the Chelsea attack.
Chelsea are also vulnerable when the opposition outside backs get involved in the attack. Neither of Chelsea's wider attacking players in Juan Mata or Eden Hazard are quick to help in the defensive end. When the opposition outside backs advance past them, it often leaves Chelsea's own outside backs left to defend two men, particularly when the opposition is playing with a winger. On United's second goal, Hazard was guilty of allowing United right back Rafael to advance past him and receive the ball, leaving Cole to try to defend both Rafael and Valencia. Cole was forced to step to ball, allowing Rafeal to play an easy pass down the line for Valencia who had the time to pick out a perfect low cross for Van Persie.
Like Chelsea, Arsenal line up in a 4-2-3-1 and have in recent weeks been susceptible to opposition attacks from wide areas, particularly down Arsenal's left side. Since the injury to left back Kieran Gibbs, his replacement Andre Santos has been poor both positionally and when asked to defend in 1 v. 1 situations. Ferguson will have certainly taken notice of how Schalke ripped apart the left side of Arsenal's defense in their 2-0 Champions league win over the Gunners last Wednesday and may well choose to once again play with a traditional right winger to exploit this weakness. Opting for Valencia once again seems like a good choice. The Columbian is an excellent option on the wing against teams that play with very attacking full backs. He is defensively disciplined and has a tremendous work rate. He will diligently track the opposition full back on defense but his work rate also allows him to break past the full back into space when United win possession back and look to counter. Alternatively, given Santos' poor 1-on-1 defending, Ferguson could go with the out-of-favor Nani. Nani is less disciplined defensively but brings to the side an ability to beat the opposition off the dribble.
Regardless of which option Ferguson goes with, it will be crucial Arsenal show more defensive discipline on the left than they did against Schalke. Time and again the German side was able to get the ball to right midfielder Jefferson Farfan and right back Atsuto Uchida in far too much space on the wing. While Santos' positioning was poor, he was given little help by left midfielder Lukas Podolski in front of him who frequently allowed Uchida to make unmarked runs down the sideline, forcing Santos to leave Farfan and step to ball. The video below from the first half shows a clear example of this at 4:06. In this passage of play Podolski had drifted to the middle and was lazily half-pressing the Schalke center backs. Cazorla had slid left to fill Podolski's position. Santos had followed Farfan as he drifted towards the middle, opening up space down the right sideline. Cazorla completely switches off on Uchida, allowing the right back to make the run into space unmarked. Huntelaar's finishing was poor on this occasion but the video highlights what was a recurring problem for the Gunners. Understanding and communication between Santos and whoever is defending ahead of him on the left (most often Podolski) will be massively important for Arsenal against United. United's outside backs will get forward and they proved against Chelsea they can punish the opposition when given the chance to stretch its outside backs.
Ferguson may also look to frequently switch the point of attack from left to right with long diagonal balls to the right wing (perhaps we could see Paul Scholes in the side for his long passing ability). Switching the point of attack will force Santos into situations where he's left to defend the right winger 1-on-1, a battle Valencia (or Nani) are always likely to win. Santos will need to be more up for the task than he was against Schalke.
Both limiting the number of chances United have to counter and effectively dealing with the counter when United do get the chance to break will be the final key factor for Arsenal. To prevent the counter they obviously need to be diligent in possession, avoiding silly giveaways in the middle third of the field (Schalke's second goal came from a poor giveaway from Serge Gnabry in midfield). But United will inevitably get the chance to break and when they do its crucial Arsenal get their defensive transition right. Like Chelsea's outside backs, both Carl Jenkinson and Santos are called upon to join the attack and provide width high up the field. This of course leaves them exposed to counter attacks down the wings when they lose possession. However, unlike John Obi Mikel and Ramires at Chelsea, Arsenal won't have especially combative, ball winning holding midfielders in front of the back four to break up counterattacks (unless Wenger makes a surprising decision and starts Coquelin alongside Arteta). The center backs and holding midfielders will therefore have to be particularly aware of their defensive shape even when Arsenal are in possession.
With the Gunners in the midst of a rather unconvincing four game spell, they'll need to improve drastically on recent performances to have any shot of coming away from Old Trafford with a result. Shoring up the left side of the defense and preventing United's wide men from getting crosses into Van Persie will be crucial in ensuring the Gunners don't experience a repeat of last season's humiliating 8-2 defeat.
