Linked with Manchester United, Sancho is also interesting Bayern ahead of the summer market.
After last night's defeat of BVB, Flick declared: "I don't like to talk about players who are under contract at other clubs. I can say that Jadon Sancho has a high quality but in the end he also makes Borussia Dortmund very, very good.
"He is a fantastic talent and has tremendous qualities.
"That's why you simply have to admit that Dortmund has a very good player there."
Sancho is expected to leave BVB this summer, with United prepared to offer him the coveted No7 shirt as part of their package.