Arsenal have confirmed that they will be without Andre Santos for the next three months after taking the decision to send him under the knife.
The Brazilian left-back suffered an ankle injury during the recent UEFA Champions League defeat at Olympiakos and was initially ruled out for three weeks.
But further investigation revealed ligament damage, and the 28-year-old requires surgery to repair the problem.
A statement from the Gunners released on Monday confirmed the prognosis, leaving Arsene Wenger without a recognised full-back for the foreseeable future.
First-choice right-back Bacary Sagna is recovering from a broken leg, deputy Carl Jenkinson has a stress fracture in his back and left-back Kieran Gibbs recently underwent a hernia operation.
Wenger fielded four centre-halves for Saturday's victory over Everton, with Johan Djourou at right-back and Thomas Vermaelen on the left.
"Arsenal Football Club can confirm that, following investigations and subsequent medical opinions by club specialists, left-back Andre Santos will have surgery to repair ligament damage in his right ankle sustained in the game against Olympiakos last week," read the statement released on the club's official website.
"Andre will have surgery in Brazil this week and is expected to be out for around three months.
"Everyone at the club wishes him well."