Arsene Wenger has revealed that Abou Diaby sustained knee ligament damage against Porto on Wednesday. The French midfielder picked up the knock during Arsenal's disappointing 2-1 defeat at Estadio do Dragao.

The Gunners are yet to determine the full severity of the problem, but accept that the 23-year-old could be set for a lengthy spell on the sidelines.

Diaby's setback has been offset by positive news regarding Alex Song's fitness, but Wenger is still expecting to be short on numbers for Saturday's home date with Sunderland.

He told Arsenal TV Online: "We lost Abou Diaby last night [at Porto]. It is not understandable. I don't know how it worked. But he has a medial knee ligament injury. We discovered it today (Thursday). He came in today and he had pain in his knee.