London, Dec 13: Arsenal's injury-hit defense took another blow Monday when left back Andre Santos was ruled out for three months with an ankle ligament injury.
Santos hurt his right ankle in last week's Champions League match against Olympiakos and will have surgery this week in his native Brazil to repair the damage.
One of few first-team regulars selected, he was forced off early in the second half of a 3-1 defeat.
The injury means Arsenal manager Arsene Wenger could head into a busy period without any recognized full backs.
Arsenal is one game into a spell of six Premier League matches in 24 days and is already without left back Kieran Gibbs because of a hernia.
Right backs Carl Jenkinson and Bacary Sagna are also injured.