The 23-year-old had been offered the chance to sign a new deal at Tannadice, along with teenage defender John Souttar.
But Ciftci, who has been capped by Turkey at U19 level, has informed United he will go into the final 12 months of his current deal and then move on.
Ciftci said: “After extending my two-year contract in December 2013 with an extra year, I have decided that after three years at Dundee United I will be looking for a new challenge.
“I’m satisfied with my development so far and therefore I must thank the coaching staff who played a big part in that. I would also like to thank the fans and the club, who have always been behind me.”
United manager Jackie McNamara is happy he will get another full season from Ciftci, who has scored 33 goals since joining the club.
McNamara said: “Nadir is a top performer for us and his worth to the team is much more than goals.
“He is a regular and this season alone played more than 85 per cent game time which is evidence of the positive and professional attitude he has on and off the pitch.
“People forget he is a young player and we are pleased to be part of his development while getting the best of him on the pitch.
“We respect his decision and his ambition as we know he’s attracted significant attention from other clubs.
“However, I’m looking forward to welcoming him back for the new season so that he can be part of a side that will once again challenge at the top of the game.”