The 20-year-old arrives after an impressive spell in the Netherlands, where he developed into a regular first-team player and attracted interest from several clubs, including fellow Bundesliga side Hoffenheim. Stuttgart ultimately won the race for his signature, strengthening their attacking options ahead of a season that includes Champions League football.
While German reports have placed the initial transfer fee at around 12.5 million euros plus add-ons, Feyenoord announced the deal is worth a guaranteed 15 million euros, with performance-related bonuses potentially increasing the total value to 17 million euros.
Stuttgart sporting director Fabian Wohlgemuth believes Sauer is ready to make the step to German football.
"Leo has repeatedly demonstrated his qualities in the Dutch Eredivisie, the Europa League and while playing for the Slovakia national team," Wohlgemuth said. "He is a player with great potential, not just because of his age. We've signed him with the conviction that he can strengthen and further develop our attacking style in the years ahead."
Sauer was equally enthusiastic about the move.
"It feels great to be part of such a prestigious club," he said. "VfB have a strong reputation, a rich tradition and a huge fan base. I can't wait to meet my new teammates and play for the club for the first time. My goal is to be as successful as possible with VfB in all three competitions."
The Bratislava-born winger leaves Feyenoord after four years with the Dutch club, having initially joined from MSK Zilina in 2022 before signing a professional contract the following year.
Following a successful loan spell at NAC Breda during the 2024/25 campaign, Sauer returned to Rotterdam and established himself under Robin van Persie last season, making 29 appearances in all competitions and scoring four goals despite spending time on the sidelines through injury.
In total, he featured 44 times for Feyenoord's first team before completing his move to Germany.
In an emotional farewell, Sauer thanked the club that helped launch his senior career.
"I am enormously grateful to Feyenoord for the trust they showed in me at such a young age and for everyone who helped me continue developing," he said.
"From the academy to the first team, I've seen what a wonderful club this is and I've been able to lay the foundations for what I hope will be a great career in Europe. I wore this shirt with pride and I hope the supporters, who always made me feel loved, will understand this step. Hopefully we'll meet again one day, perhaps even in the Champions League."
Sauer has already earned 11 senior caps for Slovakia and has previous experience against German opposition, featuring in both World Cup qualifiers against Germany last year, including Slovakia's memorable 2-0 home victory.
He is now set to begin the next chapter of his career with Stuttgart, who open their 2026/27 campaign away to Hansa Rostock in the DFB-Pokal before beginning their Bundesliga season with a trip to reigning champions Bayern Munich.
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