Ciftci joined Celtic from Dundee United in 2015, but has only scored four times in 26 appearances for the Hoops.
The 26-year-old has recently spent time on loan in Turkey and Poland, while he represented both Plymouth Argyle and Motherwell during the 2017-18 campaign.
The former Turkey Under-19 international was contracted to Celtic until the end of next season, but the Scottish champions have decided to release him a year early.
"Celtic football club can confirm that Nadir Ciftci will be leaving the club on June 30, 2018," read a statement from Celtic. "Currently on loan to Motherwell, everyone at Celtic wishes Nadir all the very best for the future."
Ciftci has not turned out for Celtic since February 2017.