Arsene Wenger has said that Andre Santos could face a lengthy absence after suffering an ankle injury during Arsenal's 3-1 Champions League loss to Olympiakos last night.
Santos left the stadium wearing a protective boot following a knock in the 51st minute of the game.
"Santos suffered a bad ankle injury," Wenger said.
"It looks like he will be out for a while.
"Hopefully Santos will not be too long but, for Saturday against Everton, he looks to be struggling."
Despite the loss, Arsenal qualify for the knockout stages of the Champions League at the top of their group.