Dortmund's season ended on a deflating note on Saturday as they were thrashed 4-0 by Hoffenheim to finish 13 points adrift of Bundesliga champions Bayern Munich.
While the club have now waved goodbye to Mario Gotze and Real Madrid loanee Achraf Hakimi, they remain hopeful of keeping hold of winger Sancho.
The 20-year-old England international is under contract until 2022 and despite being linked to a return to his homeland, Watzke doubts Premier League clubs such as United and Liverpool can pay what Dortmund want.
"There is nothing to say on Erling [Haaland], he will stay," Watzke told Sport1 of the young striker they only acquired in January.
"If Jadon approaches us and says he wants to leave no matter what, which did not happen so far, and a club wants to spend what we demand, we will discuss it.
"But I don't think there will be a club that pays the fee that we want.
"There will not be a single cent corona[virus] discount. We have passed the status, where we had to sell players. I don't think there will be a transfer next summer."
One man who will definitely be at Dortmund next season is coach Lucien Favre.
His future looked unclear as Dortmund came up short again in the title race with Bayern, yet sporting director Michael Zorc confirmed earlier this week that Favre would return in 2020-21.
Watzke reiterated that stance on Saturday - a day after Dortmund were thumped 4-0 by Hoffenheim - stating that Favre had merited another shot at the title after back-to-back second-placed finishes.
"Every coach in the world would have lost yesterday's game because it was the team's fault," Watzke argued.
"Before against Leipzig we made one of our best matches in the last few years. Lucien Favre took us to back-to-back vice-championships and he is still under contract.