Confirming the news to the Official Club Website, Town boss Joe Royle said: "Nicky's got to have a cartilage operation and is likely to be out for four to six weeks. He's due to have an operation in the next 48 hours - as soon as we can get him in, really.
"He felt it last week, not sure exactly when it happened but he's certainly not right with it and we need to clear it up as soon as possible.
"It's frustrating because he's looked very sharp. Let's hope we are getting all our bad luck with injuries over at the start of the season."