VfL Bochum are reluctant to lose teenage midfielder Leon Goretzka.
The teen is a top target for Arsenal boss Arsene Wenger, who is pushing to close a deal for Goretzka this summer.
Bochum chief Walter Schneck said: "He could be the greatest German talent for 50 years.
"It is clear only a major fee will be involved in his departure. But he has an ongoing contract with us."