The England international had seemingly been in line to join Manchester United last summer until the coronavirus pandemic hit football finances around the world.
Dortmund have allegedly reassessed their asking price for the 20-year-old, who was once valued in the region of £110m.
According to Bild, the German outfit will be prepared to accept a bid in the region of £88m in the future, a development which is said to have alerted Chelsea.
While the Blues are well stocked for options in the final third, Thomas Tuchel will naturally want to make his own signings during the next transfer window.
Sancho has contributed five goals and nine assists in the Bundesliga and Champions League this season.