By Richard Clarke

Arsène Wenger described the weekend defeat to Hull as “a big bang on the head”. If you agree with this analogy, then the headache has gone on for days.

Victory over Porto this evening will not be a panacea for all Arsenal’s ills but it would certainly be an aspirin. A temporary measure to dull the pain so natural recovery can take place.

Only time will tell if Saturday’s defeat was an accident with treatable symptoms or a malady that will linger on throughout the campaign.

Certainly one advantage Arsenal will have tonight at Emirates Stadium is renewed focus. Wenger argued his side’s bump may have been down to a little over-confidence. That will not be a problem against the Portuguese title-holders and perennial Champions League competitors.

“When you are young you think things are going to be easy,” said the manager at his pre-match press conference. “When you have a bang on the head like [we did against Hull] you have to understand the need to be consistent. And this was a big bang.

“I believe we will win this game tonight but we want to make sure we win by getting the right belief into the game. Everybody at the moment thinks we do not have the chance to win the Champions League but I believe we have enough quality to do it. That's what we want to show tonight.

“Porto had a convincing victory against Fenerbahce and, knowing Fenerbahce's team with a basis of Brazilians and Spanish, that tells you a lot about their quality. We have to take Porto very seriously.”

In the aftermath of the defeat to Hull, Wenger promised changes. In front of Monday's media he was not forthcoming about where he would make them. However he did confirm that Samir Nasri was available again after his knee problems and Alex Song would miss out with a recurrence of the hip injury he picked up in the Carling Cup last week. Abou Diaby, Tomas Rosicky and Eduardo are still absent.

Porto have had a relatively shaky start to their Portuguese League. A record of two wins and two draws is only so-so for a side who have been champions in five of the last six years. However according to Wenger, an increase in standard is the bulk of the reason for their dip.

“In the Portgusese championship some other teams are coming up,” he said. “There was a super-domination by Porto for years and years, almost for a decade.

“But now Sporting Lisbon and especially Benfica have good teams as well. So it might be a bit less easy for them. However in Europe they have a lot of experience and they have already beaten Fenerbache of course.”

According to the Arsenal manager, that win makes the Dragons seven points from the Knockout Stages. Wenger believes double figures will be enough to qualify and therefore home form will be vital.

The Frenchman was satisfied with a draw at Kyiv on Matchday One. But it will only remain a decent point if Emirates Stadium regains its status as Arsenal’s fortress.

“In this Champions League group you know you go through with 10 points,” said Wenger.

“The calculation is quite easy. You win your three home games and you are through.

“In some groups you have two good teams and two weak teams. In this group you have four strong teams. That is why home form will be vital.”

The same can be said of the Premier League of course, that's why the ghost of Hull will loom large this evening.

History suggests a home win. This is Porto’s 11th trip to England and they have never won.

Certainly Arsenal’s season cannot afford another improbable away victory at Emirates Stadium.

Copyright 2014 The Arsenal Football Club plc. Permission to use quotations from this article is granted subject to appropriate credit being given to www.arsenal.com as the source 26 Sep 2008