Arsene Wenger is facing a crisis at full-back after revealing that Andre Santos will be out of action for longer than initially expected.
The Brazilian sustained an ankle injury in Arsenal's 3-1 defeat against Olympiakos in the UEFA Champions League on Tuesday night.
Santos later revealed that he was set to be sidelined for three weeks, but Wenger does not believe it is realistic to expect him back right at the start of the New Year.
The Gunners manager will have to find a short-term solution until Santos regains fitness, with fellow left-back Kieran Gibbs still recovering after a hernia operation last month.
Arsenal's two recognised right-backs, Bacary Sagna and Carl Jenkinson, are also currently unavailable, meaning that there will be an unusual look to the back four against Everton on Saturday.
Thomas Vermaelen, Laurent Koscielny, Johan Djourou and Per Mertesacker all prefer to play in the centre of defence but two will be asked to play at full-back this weekend.
"The bad news we have is that we lost Santos for a while," Wenger said.
"The ankle injury is more severe than expected. For how long he will be out, I don't know, but it will be more than three weeks, that's for sure.
"He is definitely out of the Christmas period."
Wenger added: "With Gibbs not being available yet we have a problem on both sides, two right full-backs are out and two left-full-backs are out."