BVB stated at the weekend that Lewandowski will not be allowed to join Bayern, but Watzke has admitted the club could still decide to cash in on the 24-year-old if another team meets its valuation of the attacker.
"We want to find a good solution for all parties involved. That's why I will not say that he will definitely stay at Dortmund. I can say that he will not move to Bayern Munich in 2013, though," Watzke told Bild.
He added, "Bayern has contacted us twice by phone in the past four weeks. We only said for legal reasons that we need a formal offer for Lewandowski, but such an offer has not been made so far. A move to Bayern is a closed book.
"We will discuss everything else with Robert and his agent in the days to come. That's a matter of respect. But our explicit wish remains that Robert plays for Dortmund next season."
Lewandowski is under contract with BVB until the summer of 2014 and has refused to ink a new deal, making him a free agent next term.
Therefore, Dortmund could be tempted to sell the forward now if an offer in the region of 30 million euros comes in, with clubs such as Real Madrid and Manchester United closely monitoring his situation.