The mood at the Emirates has changed completely both on and off the pitch since the opening day defeat to Aston Villa. For the supporters, the negativity has gone, replaced by optimism and hope. Arsene Wenger appears like a man in complete control and the squad has considerable depth in certain areas. But, perhaps the biggest factor behind the alteration was the signing of Mesut Özil - the German playmaker has provided the perfect link between guile and penetration.
Wenger celebrates his 64th birthday today, despite his current deal expiring at the end of the season there's now a strong possibility he will continue at the helm. "Dortmund have grown a lot and they look a different proposition now, maybe they were a bit impressed by us in the first (group) games (in 2011), but this time they have gained confidence," remarked the French tactician to the official UEFA website.
This is Arsenal's biggest test of the season to date, they have beaten Tottenham and Napoli already, but both those teams are undergoing a transitional period after selling their star player and using the money to strengthen the squad.Last year's runners-up are also a different proposition. The sale of Mario Götze to arch-rivals Bayern Munich hasn't derailed Borussia Dortmund, but has given a significant advantage to the reigning Bundesliga champions. They have plenty of experience when it comes to replacing creative forces; Liverpool summer transfer target, who opted for the Bundesliga instead, Henrikh Mkhitaryan will look to provide the ammunition for one of Europe's best strikers.
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Both sides are missing key personnel and had players making a reappearance at the weekend. For the Gunners, Mathieu Flamini, Alex Oxlade-Chamberlain, Lukas Podolski and Theo Walcott are all out. Bacary Sagna and Santi Cazorla returned to the fold versus Norwich, the right-back is likely to start, but the Spaniard may have to come off the bench depending on his fitness.Dortmund have similar issues, though they aren't as affected in one particular position. There's long-term absentee Lukasz Piszczek at right-back, and the excellent central midfielder Ilkay Gundogan. First-choice goalkeeper Roman Weidenfeller is suspended after he was sent-off for handling outside the area on match-day one, so Mitchell Langerak will cover between the posts once more.
With Flamini out with concussion, there's a big decision to be made in terms of striking the right balance. Last season Mikel Arteta sat at the base of the midfield, operating as a 'mobile deep-lying playmaker' alongside Abou Diaby, as the Frenchman provided the strength and power around the pitch. When Jack Wilshire reemerged into the starting line-up, it disrupted the equilibrium of the team. Wenger will probably field the in-form Aaron Ramsey with Arteta, the Welshman has 11 goals already in his most prolific campaign, whilst his all-round game has also improved immensely.
The Polish connection
The right-hand side of Dortmund's formation has been one of its strongest components over the years. Fellow countrymen Piszczek and Jakub Blaszczykowski would combine in attack and defence in equal measure. With the defender absent and Blaszczykowski starting only half the matches this season due to the integration of Pierre-Emerick Aubameyang, then it's left to Robert Lewandowski to fly the flag for the Poles. The forward has two goals in this season's Champions League in as many games and has scored six in eight matches domestically. Here, he comes face-to-face with close friend Wojciech Szczesny who will aim to deny the striker whose contract expires in June.
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Pace of the game
The two sides are expected to fly out of the blocks and the opening exchanges could be pivotal in deciding the contest. Intensity and tempo are attributes the teams will try to display with the ball, providing pressure further up the pitch when the opposing defence has possession. Arsenal were particularly aggressive with their defensive line against Napoli, but with Lewandowski's speed they may not be quite so adventurous. How long Dortmund can play at their required level remains to be seen with Klopp admitting after beating Hannover on Saturday: "The game reflects the problems of the last 13 days. We played well up until we ran out of steam. Then, we stopped playing football, with one reason being the physical shape of the players."
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Bender did a superb job of keeping Napoli's Marek Hamšík quiet, bearing in mind the Slovakian isn't as astute off the ball as Özil. Not only does the 'No. 10' top the charts for assists, but his clever movement away from central areas to the wings creates space for the wide players to cut inside. Whether Bender chooses to follow him or pass the responsibility onto his full-backs, it could make the difference when looking to snuff out Arsenal's attacks through the middle.
Paul Wilkes is a freelance European football writer specialising in Spanish players and tactics, he is also the Editor of LaLigaUK