Emil Forsberg's future at RB Leipzig continues to look uncertain with his agent announcing he "wants to take the next step in his career".
The Sweden international has been heavily linked to Liverpool, Arsenal and AC Milan and publicly said this month the absence of Champions League football would not put him off a move to the Italian club.
Mintzlaff this week issued a reminder to the attacking midfielder's representative Hasan Cetinkaya, saying: "If his agent has forgotten how long Emil is contracted to us, then we will send him a copy."
"I have never experienced such an arrogant attitude," he told Bild.
"I know how long Emil's contract with Leipzig is, and also what he owes to the club.
"But it is clear: Emil wants to take the next step in his career."
