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Almunia, Wenger's regular No.1, has been ruled out of the first leg, away at the Estadio do Dragao, with a finger injury, meaning Fabianski will make a rare start. In addition to Almunia, the Gunners are also without defender William Gallas (back), midfielder Alex Song (knee), Andrei Arshavin (hamstring) and striker Eduardo (hamstring).
Arsenal were already without Robin van Persie, Kieran Gibbs and Johan Djourou due to long-standing problems, but they have at least welcomed forward Carlos Vela back into the side.
Sol Campbell looks set to make a first Champions League appearance since the 2006 final defeat to Barcelona.
