Unal has been a sensation on-loan with FC Twente this season, with his goalscoring form attracting interest from across Europe.
The Turkish youngster admits he cannot return to City next season due to UK work permit difficulties - which could see him on the move elsewhere.
Werder are targeting Unal as a replacement for veteran centre-forward Claudio Pizarro.
Twente technical director Jan van Halst admitted: “It will be difficult to keep him.
“The problem is that we do not take the lead in this case. The ball is in Manchester City's court, and we have no idea what they are going to do with him.
“For his development it would be good for him to stay another year with us."