"Me and Callum are close friends," said Sancho, speaking from Dortmund's winter training camp in Marbella. "We've played with each other at England.
"He's the next one I would say. He's very good, very talented, fast and good dribbling skills.
"I have told him the Bundesliga is a nice league. I just told him to do whatever is best for him and whatever makes him feel comfortable."