Goal exclusively revealed on Tuesday that Hamburg are weighing up a move for the 23-year-old, and initial talks have already taken place.
Holtby moved to White Hart Lane from Schalke in January 2013 but has struggled to secure a regular place in the first team.
After spending the second half of last season on loan at Fulham, Holtby returned to Spurs and has featured twice under Mauricio Pochettino this term.
"Holtby would be a great addition. It would be great if that would work,” said Van der Vaart is quoted as saying by Bild.
"Lewis is flexible, he has great qualities."