The 21-year-old is under contract at the Westfalenstadion until 2023.
Sancho was tipped to leave Dortmund last summer but a deal never materialised as Dortmund were reluctant to let him leave for under €120m and interested clubs, such as Manchester United, were unwilling to pay that much.
However, as the summer transfer window approaches, Dortmund have re-evaluated their previous valuation and reduced it to €100m.
Sources have told ESPN that there isn't a deadline this summer as to when a deal must be completed by.
Dortmund sporting director Michael Zorc said on Saturday on ARD TV that "under certain conditions" Dortmund would let Sancho leave this summer.
"Already last year, we had a gentleman's agreement with Sancho," Zorc said.
Speaking to Sport 1 on Sunday, Zorc added: "There are certain conditions which need to be met so Jadon can leave the club. Timing and fee have been and still are the deciding parameters."
In 133 appearances for Dortmund, Sancho has scored 46 goals and set up a further 62.
Despite struggling with an injury and having a slow start to the season, he has still racked up 12 goals and 18 assists in 34 matches across all competitions.
As for Erling Haaland, who has also attracted the attention of some of Europe's top clubs, Zorc was clear that his contract situation was different.
"He's been with us for a couple of years already. There is no such agreement with Erling," Zorc said on ARD TV.