Manager Owen Coyle said: "It's fair to say that Chris has suffered a bad injury and I would expect a minimum of two to three months.
"He has damaged his medial ligament and it will certainly be a couple of months before he is back. It's very unfortunate and a body blow for Chris. That's where my thoughts are because whenever he has been available he has been in my team.
"I think the world of him, both as a player and a lad and the good thing is he is at such a young age that he will come back better and stronger for it.
"There's no doubt though that it's a hammer blow for him. He was all set to take the Premier League by strom, and he will when comes back."
There was some good news for the Clarets with Steven Caldwell returning to training today for the first time since the groin injury he sustained playing for Scotland three days before the Premier League season got underway.