Roy Keane has been a fan of the player he once played with in the Irish set-up, and the Sunderland boss has made it known he is looking for quality in the summer transfer market.
But ... can he coax the 29-year-old to the Stadium of Light with a bid of around £4m?
Keegan has a winger on his shopping list, but many believe it is to replace the "want-away" Frenchman Charles N'Zogbia, not Duff.
The ex-Chelsea player was a substitute in the Tyne/Wear derby on Sunday, and he looked bright right from his introduction, at a time Keegan wanted a spark to lift his side back to their first-half form.