Arsenal suffered a double injury blow in defeat to Olympiakos.
Gunners boss Arsene Wenger confirmed: "Fabianski felt a deep cut on the knee and Santos suffered a bad ankle injury. He looks like he will be out for a while. We have Gibbs coming back in two to three weeks. Hopefully Santos will not be too long but, for Saturday against Everton, he looks to be short. We have as well Vermaelen who can play in his position."