Sahin was voted the Bundesliga's player of the year when Dortmund won the title in 2010/11 before he joined Real Madrid.
After failing to hold down a regular berth in the Madrid side, Sahin moved to Liverpool on a season-long loan, although he is still contracted to the Spanish club until 2017.
The Turkey international has failed to rediscover his best form and Dortmund are monitoring his progress.
"Of course we are following Nuri's career - he's one of our lads," Zorc told the Bild newspaper.
"We said to him back then (when he left), if Nuri says that he wants nothing other than to play in Dortmund, then we will deal with the issue.
"But it has got to be manageable, and nothing has changed in that regard."
Dortmund have said they would not sell attacking midfielder Mario Gotze under any conditions.
"Mario has a long-term contract with us and he feels very happy here with his family and friends in Dortmund," Zorc said.
"There is nothing that suggests that will change. He is 20 and, consequently, far from reaching the end of his development."