The 23-year-old German left Schalke for Tottenham a year ago, but has only been on the fringes of the first team this season.
Holtby is desperate for regular football as he attempts to revive his faint hopes of a World Cup call-up and a move back to his home country could catch the eye of selectors.
Agent Marcus Noack has suggested that Holtby could return to Schalke before the end of the month, with a loan until the end of the season being the most likely option.
"Lewis is desperate to play, which is why we are looking intensively for solutions," Noack told the Bild newspaper.
"Schalke is an interesting option."
The Bundesliga side could be in need of another midfielder as Jermaine Jones has requested a move away from the Veltins Arena.