Holtby underwent a medical with the German club earlier on Monday before completing the formalities to return to the Bundesliga.
Holtby signed for Spurs in January 2013 from Schalke but has struggled to establish himself in the starting line-up at White Hart Lane.
A six-month loan spell at Fulham last season proved unsuccessful as the Cottagers were relegated to the Championship and manager Felix Magath criticised Holtby's attitude.
Mauricio Pochettino's arrival as Spurs head coach offered renewed hope for the midfielder but despite a promising pre-season campaign, Holtby has not started any of Tottenham's three Premier League matches so far.
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