Arsenal will try to become the first English club to win at the Stadium of the Dragon when it takes on FC Porto on Wednesday in the round-of-16 in the Champions League.
The Gunners have played entertaining football this season but have lacked consistency in the Premier League and have already exited the FA Cup and League Cup, meaning the Champions League could be their best chance of ending a five-year title drought.
Recent defeats against rivals Manchester United and Chelsea raised questions about Arsenal's title credentials, with the team looking especially vulnerable against counterattacks and set pieces.
A win over Liverpool lifted Arsenal to third in the league and restored confidence but in Portugal it will meet a club which boasts an impressive European pedigree.
Porto, a two-time European champion, is into the last 16 for the sixth time in seven seasons. Last season, Porto beat Arsenal 2-0 in Portugal in the group phase.
"This game is wide open. It could go either way," Porto coach Jesualdo Ferreira said. "This match is an important test of our true quality. We really want to reach the quarterfinals, and this is one of the most difficult opponents we could have come up against."
The Gunners were beaten finalists in the 2006 Champions League and last season reached the semifinals only to be trounced by Manchester United.
Arsenal midfielder Andrei Arshavin is expected to miss the match but forward Eduardo and midfielder Alex Song could be fit.
Porto is still in the running for four trophies. As well as the Champions League, the team is unbeaten at home to sit third in the league, and have advanced deep into the two Portuguese cup competitions.
But the impressive record conceals what has been a disappointing run of form for a club which has won the domestic title for six of the past seven seasons. A 0-0 draw last weekend against lowly Leixoes left Porto nine points behind leader Benfica.
The addition during the January transfer window of playmaker Ruben Micael has brought a marked improvement in Porto's fluency, though Micael has a bruised shoulder and could miss the Arsenal match.
Midfielder Cristian Rodriguez is also in doubt but Portugal's Raul Meireles should return.
With Ernesto Farias and Orlando Sa struggling to shake off injuries, Ferreira has only Colombian Radamel Falcao available as a center forward.
Brazilian striker Hulk, who has been suspended from Portuguese league games since Dec. 20, is likely to be on the bench.
"FC Porto has a a strong record and a certain stature in this competition," defender Bruno Alves said. "Arsenal is well organized and has world class players. They're strong in every part of the pitch, though (Cesc) Fabregas is obviously a class player and crucial in their attacking buildup. "
