Holtby confirmed late last week that he was leaving the German side and would be joining Spurs at the end of the season when his contract expires.
But that deal could now happen in the January transfer window if Tottenham come up with a fee believed to be £1.6m.
Schalke's managing director Horst Heldt said: "If Tottenham ask for Holtby in the January window, we will talk to them about it.
"Nothing has happened yet, but, from our point of view, we are prepared to speak to them.
"It would have to be done quickly, because we would have to find a replacement for him."