The former Burnley man picked up a knee injury on his return to the first team in the League Cup win over Sheffield Wednesday, and is expected to miss another month and a half
The news will come as a severe blow to the 23-year-old, who had only just returned from an ankle injury sustained in a pre-season friendly against Bristol City.
The former Chelsea trainee expressed his disappointment over Twitter, stating: "[Out for] another four to six weeks with my left knee. Luck's just not going my way this season. It could be worse but I was so close to getting back from the ankle."
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Cork was an ever-present last season, playing in all 46 league games for the Saints on their way to securing promotion from the Championship and went on to represent Team GB at the London 2012 Olympics.