Lukas Podolski wants to return to Arsenal when his loan expires at Inter Milan, according to manager Roberto Mancini.
Neil Redfearn has taken heart from Leeds' claims that their young first-team players will not be sold in the summer.
Duncan is regarded as one of Ghana's most promising young players and has been compared Chelsea's Michael Essien.
A move to the Stadium of Light has been mooted this summer, and the 20-year-old claims he is aware of the reported interest from Wearside.
Duncan said: "I am flattered by the interest of Sunderland. I know the scout of Sunderland has been watching me.
"To be honest, though, nothing has been done and Inter will have a big say if I leave Inter or not.
"Fans compare me with Essien and if I can have half of his career I will be very happy.
"He is the best midfielder ever in Ghana. He played box-to-box, could break play up and could dictate play at the same time."