The 28-year-old joined Cagliari in the January transfer window from Fiorentina on a short-term deal until the end of the season.
Duncan played a key role for the Cagliari in their battle to escape relegation in the just ended Serie A season.
Cagliari finished 16th on the league table with 37 points to avoid being relegated.
The Ghanaian International after his loan stint at the club has thanked the President as he returns to Fiorentina.
“Thanks to the president and @cagliaricalcio for this great experience in which there was the beauty of this sport between suffering and joy. It has certainly given me a lot and I have also learned a lot by getting to know these people. Thank you all for messages and support from day one. However my future will be, I will always be a fan of this family! Goodbye and come on Casteddu”, Duncan said in a post.
Alfred Duncan made 19 appearances for Cagliari in the just ended campaign.
