The Poland international has been widely linked with a move to Bavaria, but his club are keen to hold on to him as the striker refuses to discuss his future
A number of recent reports suggested that the Bavarians are close to agreeing personal terms with the Poland international, but Watzke has insisted that BVB have no intention to let go of the prolific striker.
"This is nothing but speculation. There's zero substance in the reports and there's not even a primary source," Watzke told reporters.
"The fact is that Robert has a contract with Dortmund until the summer of 2014, and we want to extend his stay.
"We will sit down and discuss what to do next if he hasn't signed a new deal by the end of the season, but we will definitely not let go of him for just any price."
Meanwhile, the 24-year-old attacker has insisted that he will not make a decision on his future any time soon.
"It's nice that clubs are interested and make enquiries, but I have told everyone that I don't want to hear anything about it until the end of the season. I am focused on Borussia Dortmund," he told Sport Bild.
"I will listen to everybody in the summer when I sit down with my agents. I don't care about all the speculation. I will make my decision at the end of the season."
Lewandowski has netted 13 goals in 19 Bundesliga appearances so far this season.