The 25-year-old midfielder suffered the problem on the eve of his side´s Barclays Premier League defeat at Wigan on August 18 and it was initially thought he would only be out for six weeks.
But Keane told the club´s official website: "It looks as though Deano will need surgery in a couple of weeks. It looks like it´s a cruciate so that would rule him out for six or seven months. It´s been a bad day. It´s a bitter blow. We are missing his leadership qualities and his presence."
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