Dortmund are thought to have valued Sancho at £109m last summer, while Haaland's asking price could be in excess of £115m as a release clause in his contract does not come into play until the end of next season.
Watzke has admitted that he cannot "rule anything out" this summer due to the financial impact of the coronavirus outbreak, which has weakened the club's finances.
BVB are also facing the possibility of missing out on Champions League football for next season as they currently sit down in sixth position in the table, six points off the top four.
"In the midst of a pandemic, I no longer rule anything out," Watzke told Handelsblatt. "But it is not necessarily aspired to. Above all, there is the financial balance: that we have a strong team on the field and are economically stable at the same time.
"Asking banks for credit lines at the drop of a hat just to avoid selling a player will not be our way."