Marco Reus will make a decision on his future within the next few weeks.
Reus is under contract until 2017, but he has a €25 million trigger clause in his contract.
Dortmund have tried to buy the release clause off him, but have so far not succeeded.
"I still have the hope that he stays with us for a long time," BVB CEO Hans-Joachim Watzke said. "But if he decides differently, that's the way it is. One of the challenges in football is to benefit from changes in the squad or create other things."
Barcelona, Real Madrid, Bayern Munich and others are all interested in Reus.