The Ireland international limped off during The Addicks 4-2 defeat at West Brom and will now miss the hectic Christmas period and most of January, which will include a crucial trip to Vicarage Road to play league rivals Watford.
It is a massive blow to Alan Pardew's side for Saturday's game against Hull at The Valley, especially with top scorer Chris Iwelumo, Chris Powell and Darren Ambrose doubtful.