Gary McAllister said: "It's a bit of bad news, but Andy has a problem with a knee. He's been to see a surgeon and we're going to decide which way to go about sorting it out.
"The knee might need a little bit of a scrape or a clean and that's something for the medical people to sort out. But, Andy being a fit guy, we are looking more in the region of two to three weeks out even if the worst comes to the worst.
"He's a player who gives us a bit of momentum. He's a driving force in the middle of the park, but we're well covered in the middle of the park and now it will be up to others to pick up that mantle."