Reus has a £20m buy-out clause in his contract, which expires in 2017, and has refused to sign an extension so far.
Real Madrid are favourites to secure his transfer, however, Dortmund have expressed an interest in signing Chelsea's Andre Schurrle, who was subject of a £23.5m bid from Wolfsburg last week, as a potential replacement.
Dortmund chief executive Hans-Joachim Watzke said: "I can understand Marco. He first wants to play again and then he wants to see which direction to take.
"I have a legitimate hope that he will stay for the long term. If not, it is something we will have to accept."