The midfielder has left Tottenham for a temporary move away for the second time, with the Bundesliga outfit able to make the move permanent at the end of the season
Goal exclusively revealed in August that the Bundesliga outfit were eyeing a move for the German, with Hamburg retaining the option to make the move permanent at the end of the season.
A permanent contract starting in 2015 has already been agreed and would require no negotiations should the German side activate the clause to buy him at the end of this campaign, Goal understands.
The 23-year-old spent the second half of last season at Fulham after falling out of favour under both Andre Villas-Boas and Tim Sherwood and has been afforded just one substitute appearance under new boss Mauricio Pochettino this term.
Cristian Eriksen, Erik Lamela and Nacer Chadli are currently ahead of Holtby in the pecking order and the attacking midfielder was an unused substitute in recent Premier League clashes with QPR and Liverpool.