The Pole's deal expires in June 2014, and he has been closely linked with a move to Bayern Munich, Manchester United and Juventus amongst other clubs.
The club's general manager, Hans-Joachim Watzke, claimed earlier this week he believes the 24-year-old would opt to stay, but his colleague does not share his optimism.
|11/4||Robert Lewandowski is 11/4 with Bet365 to be top scorer of the Bundesliga this season|
"We must say this. Apart from that, we are very relaxed and we will be prepared for every eventuality."
Coach Jurgen Klopp added he was confident his side would be fine should the star striker elect to leave the club.
"If Lewandowski were to go, we are prepared," he told ZDF.
Lewandowski is currently serving a three-game ban after his red card against Hamburg last week, but Dortmund were able to beat Eintracht Frankfurt 3-0, despite his absence.