German daily Bild reports, via Talksport, that Holtby's agent Marcus Noack believes it would be an interesting move for the German midfielder as he bids to secure a World Cup place:
“Lewis is desperate to play, which is why we are looking intensively for solutions,” Noack said. “Schalke is an interesting option.”
Holtby has made just 10 league starts and scored one goal for Spurs in all competitions since joining, while in his time with Schalke he scored 10 goals in 44 starts, per Soccerbase.
Holtby has not featured for Spurs since a 1-1 draw with West Brom on Boxing Day, and Goal UK feels he could become part of a January clear-out by new Spurs boss Tim Sherwood:
Competition is rife for a place in Spurs' midfield with Moussa Dembele, Aaron Lennon, Christian Eriksen, Etienne Capoue and Nacer Chadli all preferred to the youngster in recent weeks.
Holtby made three appearances, scoring one goal at last summer's UEFA European Under-21 Championships, and first-team football is a must if he wishes to break into the senior squad.
Right now, he cannot compete alongside the likes of Mesut Ozil, Bastian Schweinsteiger, Mario Gotze, Toni Kroos and Thomas Muller, to name but a few in the full German national setup.
Several players have returned home in recent years, so Holtby should feel no shame if he returns to the Bundesliga.
Thierry Henry returned to Arsenal on loan in 2012, firing the winning goal against Leeds United in the FA Cup on his return. Shinji Kagawa is another who may need the comforts of the Bundesliga to rediscover his best form.
Sometimes it is good to return from whence you came. And maybe that is what Holtby needs to revive a promising young career.