The 27-year-old Ghanaian midfielder joins Casteddu until the end of the season with an option to extend further.
Duncan’s move means he’ll have turned out for six teams in Serie A by the time he makes his debut for the Rossoblu, having amassed 195 games and scored nine times in Italy’s top flight since making his bow for Inter in 2012.
The combative central midfielder will add much-needed guile and determination to Cagliari as they look to pull away from the drop zone. Eusebio Di Francesco’s side presently sit just one point off the bottom three.
The Sardinians have wasted no time in getting the player in amongst the action with him named in Monday’s squad list for their home tie against Scudetto-chasing Milan.