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.
And Voller has reaffirmed Havertz will only leave the club if their demands are met.
"No decision has been made yet," the Leverkusen chief told German outlet Kicker while discussing Havertz’s future. "I’d like to repeat myself by emphasising that we’re talking about a wonderful footballer.
"There is nothing new in this regard. We have a clear and mutual agreement with him and his representatives that he can only leave if certain requirements are met. Otherwise he will stay."
Lampard spoke of his desire to recruit new options after Chelsea's crushing 4-1 (agg. 7-1) defeat to Bayern Munich in the Champions League round of 16 last week.
"We will look at that because that’s our job, my job and we’re very joined up with how we’ve worked at it already," Lampard said.
"From having a transfer ban, you feel the fact we missed out where other clubs had spent and improved and recruitment is a big part of this game.
"Nights like tonight for me from a footballing sense show me a lot so it’s a conversation now the season is ended.
"It’s a very quick turnaround but now is the time to see what areas we can improve in."
But the Blues boss kept his cards close to his chest when quizzed about the possibility of signing Havertz, adding: "I wouldn’t expect anything but it’s our job to go away and see what happens and see where we can improve.
"In a footballing sense, I feel like I know where we can improve but now it’s time to look at that."
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