Spurs coach Steffen Freund previously spoke highly of former Schalke winger Holtby's potential.
Although Freund has not worked directly with Holtby, he is aware of the player's talents from his time coaching Germany's Under-16 and Under-17 sides.
"For Lewis it will not be a problem (adapting to English football)," Freund said.
"He is half-English, he loves the Premier League. He is captain of the Under-21s for Germany, he will lead the team at the European Championship in Israel.
"I worked for Under-16s and Under-17s for the last three years, that is why I don't know him really well but what I can say is that he is a really good player."
It is understood Holtby has signed a four-year contract at Spurs that will expire in June 2017.