Hertha Berlin have informed Bundesliga rivals Stuttgart that Gojko Kacar is not for sale at any price.
The Serbian starlet was among those to catch the eye at this summer's European U21 Championships, helping to raise his profile.
He is now regarded as one of the finest young talents in Europe and interest in his services has come as no surprise.
Hertha, though, have no intention of parting with the 22-year-old midfielder and have sought to warn off any potential suitors.
"We will not transfer Gojko Kacar, we will not sell this player at any point," Hertha general manager Michael Preetz told Stuttgarter Nachrichten.
"This particular stance is not negotiable."
Stuttgart general manager Horst Heldt insists his side have other alternatives in mind after being warned off Kacar.
"This is not something that is going to worry me, we are always looking at different options," he said.
"We will see what we can do in the remaining time left in the transfer window. But there will be no big deal."