Arsenal left-back Andre Santos has been ruled out of action for three months with the ankle injury he picked up against Olympiakos.
The 28-year-old will require surgery after being forced off after 51 minutes of the 3-1 defeat in Tuesday's final Champions League group fixture.
The Gunners have confirmed Santos will have ligament damage in his right ankle repaired in Brazil this week.
Full-backs Carl Jenkinson, Kieran Gibbs and Bacary Sagna are already injured.
Gibbs is recovering from last month's hernia operation and is not expected to return for at least another fortnight, while Jenkinson is out with a stress fracture to his back.
Sagna broke his leg in a defeat by Tottenham in October.
Thomas Vermaelen lined up at left-back in Saturday's 1-0 win over Everton as Arsenal fielded a back four made up entirely of central defenders.
Santos, who has 22 caps for Brazil, moved to the Gunners this summer from Turkish side Fenerbahce in a £6m deal.