He has had surgery three times this season in efforts to rectify the issues and Jol fears the former Real Madrid midfielder's career could be over.
Jol revealed the 31-year-old faces a further five or six months on the sidelines, but the club will continue to pay for his treatment in an effort to save his career. Jol said: "He is worth giving that chance.
"He was a top, top player - he played a long time with Real Madrid. He will have a chance to prove he is fit and if he does we will try to keep him for the next six months."