Stiller has established himself as one of the Bundesliga's most reliable deep-lying midfielders in recent seasons, and according to German outlet Fussball News, Barcelona and Juventus are showing particularly strong interest in the 25-year-old ahead of the January window, with both clubs having sent scouts to watch him during VfB Stuttgart's Champions League opener against Viking FK.
Arsenal and Bayer Leverkusen have also registered their interest in the Germany international, though the report indicates all four clubs remain in an early observation phase, with none having opened formal talks with Stuttgart.
Stiller, who came through Bayern Munich's academy before moving to Stuttgart, has a contract running until the summer of 2028, giving the Bundesliga club a strong negotiating position. Stuttgart are said to be seeking between 40 and 50 million euros for his signature, reflecting his growing importance to the side both in build-up play and in controlling matches from deep midfield.
Across 137 competitive appearances for Stuttgart, Stiller has scored seven goals and provided 28 assists, underlining his creative influence from a deeper role. He has also made nine appearances for the German national team, continuing to build his international profile alongside his club form, having progressed through Germany's various youth age groups before earning his senior debut in recent seasons.
None of the interested clubs are believed to have made any concrete approach so far, and a move before the winter window looks fairly unlikely given the early stage of scouting activity. Stuttgart, who face Bayern Munich's continued interest as well given Stiller's boyhood connection to the club, are not thought to be actively looking to sell, and any transfer would likely require a significant improvement on their stated valuation to tempt the club into negotiations.
Stiller's future is expected to become a bigger talking point if he continues to perform at his current level, with a move abroad reportedly appealing to him more than a switch to domestic rivals Bayer Leverkusen, should he decide the time is right to leave the Mercedes-Benz Arena.