The German midfielder left White Hart Lane on loan this summer to return to the Bundesliga, where he will play alongside former Tottenham man Van der Vaart.
And the 31-year-old has welcomed Holtby to Germany with some kind words in the wake of his move - which could be made permanent at the end of the current campaign.
Indeed, Van der Vaart believes the midfielder will be an 'important player' for Hamburg and praised his technical skill, as well as his tackling ability.
“Lewis Holtby is a really good player. We need players like him,” the Hamburg captain said.
“He is technically good but also good at tackling. I feel that Hotlby will be an important player for Hamburg this season.”
Since new boss Mauricio Pochettino took over this summer, the Spurs squad has seen numerous changes, both in terms of new signings and player departures.
Holtby, then, is just one of the Tottenham midfielders to have been moved on during the transfer window, with Sandro also joining Queens Park Rangers and Gylfi Sigurdsson moving to Swansea City.
The difference with the 23-year-old, however, is that he could still return to north London come the end of the season.
Van der Vaart will no doubt hope that isn't the case, though.