Santos blow for Arsenal
The left-back sustained the problem in last week's 3-1 UEFA Champions League defeat against Olympiacos in Greece.
A statement on the club's official website read: "We 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 Olympiacos last week.
"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."
The 28-year-old Brazilian joined the club in August and has made 14 appearances, scoring in the 5-3 Barclays Premier League win at Chelsea and the 2-1 home defeat of Olympiacos in north London.