Bayer Leverkusen sporting director Rudi Voller insists Kai Havertz will only leave the Bundesliga side this summer if "certain requirements are met".
Havertz is the subject of huge interest from Chelsea as manager Frank Lampard looks to further strengthen his options in attack.
The Germany international scored or assisted 27 times during an eye-catching campaign and is reportedly ready to sign a five-year deal at Stamford Bridge.
But Leverkusen are refusing to lower their €100million (£89.8million) asking price for the 21-year-old, who has two years remaining on his deal at BayArena.
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