Naletilic had also previously hinted at interest from Liverpool as well as other clubs in England, Italy and France.
Pjaca joined Juve at the start of the 2016-17 season, but suffered a cruciate ligament injury that ended his debut campaign in March 2017.
The Croatia international has since failed to make a single appearance for the Italians this term, and has now been declared surplus to requirements.
Schalke's move to bolster their forces in the middle of the park, meanwhile, comes at a time when two homegrown playmakers look set to leave.
Max Meyer and Leon Goretzka are out of contract at the end of the season, with the latter strongly linked with a move to Bayern Munich.
And while the future of those two stars is up in the air, Pjaca's arrival will be a boost to a side that currently sits a distant second behind Bayern in the Bundesliga standings, as they look to consolidate a fine first half of the season and insure Champions League qualification.