Arsene Wenger has confirmed that Arsenal will have to do without Mathieu Flamini in their Champions League clash with Borussia Dortmund on Tuesday.
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Victory against Dortmund would put the Gunners on nine points and leave them on the threshold of qualification from the group stages.
However, Wenger will have to reshuffle his midfield with the loss of Flamini, but will not make any decision on his team until the day of the game.
"Flamini is doing well, he has practised normally but we will not play him [on Tuesday] because there is a five days rule that we will respect, not to take any chances," Wenger said.
"It was a concussion and the doctor advised us not to play him. He will be OK for the weekend."
Wenger admitted there may be other changes to the side that beat Norwich 4-1, adding: "A little bit, certainly yes, but I leave myself 24 hours until tomorrow afternoon to decide that,” he said.
"It is an important game of course. It is not a decider but it's an important one. It's an 80 percent game for me, for the qualifier. If we win the game and we win the other home game we know we are there."
To do that, Arsenal will have to keep striker Robert Lewandowski quiet, a player the club have been linked to.
He is a close personal friend of Poland international teammate Wojciech Szczesny, and the goalkeeper said they are in in contact with each other daily.
Lewandowski has endured something of a difficult time with his country of late, missing a series of opportunities in the 2-0 defeat that secured England's qualification for the World Cup, but Szczesny believes he is still one of the continent's top strikers.
He said: "I think certainly Lewandowski is one of the best you can find in Europe so he will be dangerous but we played against them before and we've handled him quite well so I hope we can do that again.
"Me and Robert are very good friends, we speak on a daily basis and he's excited to come here, I'm excited to play against him and it will be a good challenge. We will forget the friendship for now and I'm sure it will be fine after the game.
"It makes it more exciting but other than that I'll treat it like every other game and be professional and prepare in the same way and hopefully get the same result that we've been getting recently.
"He's had a tough time with the national team but when you look at his goalscoring record in the Champions League and Bundesliga last year you can see how good he is.
“He is a goalscorer and that's what makes him a good striker. He did it when he was in Poland and since he signed for Dortmund he has always been around the top goalscorers. That's what he does, it's as simple as that."