By Richard Clarke

For the first time this season, Arsenal have to react.

The defeat to Chelsea on Saturday, and more importantly the way it was inflicted, has inserted the first question mark into campaign that had, if not quite word-perfect, at least said all the right things to the supporters.

On another day, Arsène Wenger’s side might have snatched a draw at the weekend to maintain their momentum.

But a responsive victory against Olympiacos on Wednesday will at least in ensure Saturday was a comma, a pause for thought, in an otherwise onward journey.

Rather than a full stop.

“Yes, the players are disappointed we lost the game,” admitted Wenger at his pre-match press conference. “But we have a Champions League game in front of us at home and we want to put things right. There were a lot of positives in the Chelsea game as well and what was not good is easy to correct.

“The title race is long but we have to make sure the Champions League is long for us as well.

“So yes it is about how we respond. I have been impressed by the mentality of my team but ‘mentality’ is as well about how you respond to disappointment. I am confident we will do that well and that is what we want to show now.

“The Champions League is simple - you need one away win and three home wins. We have done the first part of the job, now the second part is to be strong at home. It is only a big advantage to have an away win if you are efficient at home. That is what is at stake for us.

“Olympiacos are already in a position where their backs are against the wall because they have lost at home and, in this Champions League, it is very difficult when you lose at home. But they are highly motivated because they know they have to give everything to make it through.”

Wenger will be without Abou Diaby due to a thigh injury sustained in the early stages on Saturday. Mikel Arteta lasted the game but is a serious doubt with an ankle problem. He faces a fitness test.

Pass or fail, the manager will alter his line-up.

"I will make changes again,” he said on the eve of the game. “I will sort that out overnight."

They may include the recall of Olivier Giroud after his start at Montpellier on Matchday One. The French striker does not suffer from the anonymity many new attacking players are afflicted by when they come over. For the likes of Thierry Henry and Robert Pires, games just passed them by in the early days. There were no eye-catching mistakes but, at the same time, no notable contributions until the English autumn had fully taken hold.

At places like Liverpool, Stoke and Montpellier, Giroud’s willing work-rate was a noticeable asset. His is a contribution that will never truly be weighed in goals but, as Wenger accepts, that is a striker’s currency. He broke his duck against Coventry last week but, at the same time, has missed crucial opportunities.

"He is still in what I consider an adaptation period,” said Wenger. “It is a different team, different way of playing and different football. There is 100 per cent commitment from the centre backs here. They really go for it.

“He will adapt I’m sure. He had a chance against Liverpool, a chance against Sunderland, a chance against Chelsea. He is upset. I told him not to worry but you can say what you want. A striker who doesn't score, doesn't really listen to you. They run it through their minds over and over again."

Olympiacos are familiar foes in the Champions League; this is the third time in four seasons these sides have been pitched together in the group stage.

The stereotype suggests the Greek outfit are solid at home yet struggle on their travels. The results against Arsenal bear that out but not the games themselves. Both home victories, 2-0 in 2009 and 2-1 last year, have been hard fought. Both of the away defeats, 1-0 and 3-1 respectively, have been when a much-changed side is seeing out a group Wenger’s men have already won.

Olympiacos arrive in London in danger of being cut adrift in Group B after that opening-night defeat at home to Schalke. But they have registered five straight wins to kick-off their defence of the Greek title, hitting 13 goals in the process.

That would suggest they have adequately covered the loss of striker Kevin Mirallas to Everton. At the other end, former Manchester United Roy Carroll is the first-choice keeper. Apart from that, the threat to Arsenal will be a familiar one.

“Basically it is the same team at the back from last season,” said Wenger. “Twelve months ago I think they had a difficult start against Marseille but after that became stronger and stronger through the competition. It looks similar this year, they had a difficult start at home against Schalke and if you analyse their team it is 90 per cent the same as last season.”

A similar result will do as well. But at this stage of the season you can view performance and scoreline through the lens. For example, after six games, Arsenal are only two Premier League points better off than last season. It is the quality of their play that makes it feel so much better.

Only the Invincibles of 2003/04 have not had to reply to a Premier League defeat. It is a given, par for the course.

Response is requisite in a season and, on Wednesday, Arsenal have the opportunity to start moving forward again.

Team news:

Arsenal: Arteta (doubt – ankle), Szczesny (ankle), Diaby (thigh), Rosicky (tendon), Fabianski (back), Sagna (leg).

Olympiacos: Modesto (doubt – thigh), Torossidis (thigh), Fejsa (groin), Papazoglou (shoulder), Djebbour (thigh).

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 3 Oct 2012