Almunia to miss Partizan trip
Pole Lukasz Fabianski will replace Almunia, who suffered the injury when saving a West Bromwich Albion penalty in Arsenal's shock 3-2 home defeat in the Premier League on Saturday.
Almunia was criticised for West Brom's second goal but manager Arsene Wenger stood by his number one goalkeeper.
"(The keeper) is always the easy target, the easy scapegoat. But we win together and we lose together even if people think he made a mistake," Wenger told the club's website on Monday.
"For what happened, everybody will criticise Almunia but if we are 0-0 at half-time it is because of Almunia," the Frenchman added.
Arsenal won their first Champions League match against Braga 6-0 and lead Group H on goal difference from Ukraine's Shakhtar Donetsk.