The 18-year-old suffered a recurrence of the cartilage problem that required surgery at the end of last season and is now looking at another two months on the sidelines.
“I’m devastated to get the injury because it has put me right back with my fitness work,” Ferrell told the club’s official website.
“The medical staff have looked at it and after I had a scan on Tuesday they decided to operate on it.
“I’m gutted because this is a massive season for me as it’s my last year and I’m fighting for a contract. I’ll be out for two months then I’ll have to start from scratch again.”