The 29-year-old Republic of Ireland international has now undergone surgery to correct the problem which has sidelined him since November last year.
Manager Gus Poyet: "He has had the operation. Everything went all right, he is fine, so he starts his recovery next week.
"It's difficult to put a time on it because in the end, it was better than we thought.
"Initially when they went in and they checked, it was not as bad as they thought, so it probably be shorter, but it's difficult to say a time."