The club are now considering the offer, which is understood to have been made by a Premier League club.
However, the identity of Duff's suitors is not yet known.
Duff cost Newcastle £5m when he joined from Chelsea in the summer of 2006.
The club are now considering the offer, which is understood to have been made by a Premier League club.
However, the identity of Duff's suitors is not yet known.
Duff cost Newcastle £5m when he joined from Chelsea in the summer of 2006.