Duff will have a scan which will reveal just how long he is going to be sidelined, but the report on "Look North" on Tuesday suggests a lengthy lay off.
Craig Moore also suffered injury at Arsenal on Saturday.
Glenn Roeder: "Duff and Moore will both have scans tomorrow when the swelling goes down on their injuries and if I was to say how long we will be without them I would be only guessing.
"To be honest, while it is a case of wait and see, Craig Moore looks as though he will definitely miss our UEFA Cup tie on Thursday.
"Celestine Babayaro is not under consideration for Celta Vigo or Portsmouth on Sunday, and while Stephen Carr is making good progress from his toe injury it is debatable whether he will be ready for Thursday."