Bundesliga champion Borussia Dortmund will make its return to the Champions League after more than eight years away when it hosts Arsenal in Group F on Tuesday.
Dortmund's buildup has been overshadowed by the loss of its 18-game home unbeaten run, which ended Saturday when promoted Hertha Berlin won 2-1.
Dortmund's problems pale in comparison to Arsenal, however, which has endured a tough start to the season. Only a goalkeeping blunder from Swansea allowed Arsenal to earn a 1-0 win Saturday, its first victory of the Premier League season.
"The confidence is back now," Arsenal coach Arsene Wenger said. "We just had not won yet in the league and that had played a big part in our heads."
It was Arsenal's first outing since an 8-2 humiliation at Manchester United before the international break.
Poland goalkeeper Wojciech Szczesny was the subject of some gentle teasing from Dortmund's Polish internationals in the wake of that defeat, but has refused to let the words from Robert Lewandowski, Jakub Blaszczykowski and Lukasz Piszczek affect him.
"After the game I hope I will be the one who comes out on top," said Szczesny, who was outstanding in Poland's 2-2 draw with Germany. "They can't get in my head, I will be focused."
Dortmund coach Juergen Klopp said Sunday he had "no anticipation" for the Champions League following defeat the day before, but added, "surely it will come."
Influential playmaker Mario Goetze was suspended for Hertha's win, due to a red card from Dortmund's previous game at Bayer Leverkusen, but he will be available for Arsenal.
"Sometimes in such a game you need a knot-picker," said Klopp, highlighting the 19-year-old's importance to his side.
Arsenal is aware of the damage Goetze can do. German media say the Premier League side had a 40-million offer turned down for the Germany international in the offseason.
Arsenal did boost its defense with the arrival of Germany defender Per Mertesacker on the final day of the transfer window. The former Werder Bremen captain knows how it is to play in front of the "yellow wall" of fans in the south stand of Borussia's 80,720-capacity Signal Iduna Park.
Fellow new signings Mikel Arteta, Yossi Benayoun, Andre Santos and Park Chu-Young could also make their Champions League debuts for Arsenal.
Ivory Coast forward Gervinho and Cameroon midfielder Alex Song will be available as their three-match suspensions were only for domestic games.
"In our job, momentum is vital. We just want to play to win," Wenger said. "When you look back when we traveled to Udinese (for the Champions League playoff), everyone expected us to win the game and we did. We want the same against Dortmund."
Defender Neven Subotic feels Arsenal's open game may suit the home side.
"It's often the case that we have more attacking opportunities when the opponent wants to play football," Subotic said. "But it's the first time in the Champions League for many of us. It's a whole other level to the Bundesliga, and we'll see how we do."
Olympiakos hosts Marseille in the other Group F game.