Germany international Havertz is reportedly keen on a switch to the Blues, who have long been linked with a move for the 21-year-old.

Havertz is said to be in favour of a move to Stamford Bridge but the two clubs still seemingly have work to do to strike a deal.

Leverkusen is claimed to want £90 million ($148.5 million) for Havertz, with Chelsea thought to be interested in a structured deal that starts at around £70 million ($115.5 million).

But sporting director Voller said simply any club wanting to buy Havertz must pay the asking price otherwise he will stay at Leverkusen for another year.

Asked if Leverkusen has agreed to sell Havertz, Voller told La Gazzetta dello Sport: "No, but with his talent, it means he's on the list of all the best clubs.

"We know of the interest of a couple of clubs, especially Chelsea, but for us, the situation is quite simple: he has a two-year contract, if anyone wants him on our terms, fine, otherwise he stays here another year and we are happy.

"It won't be easy, but for an artist like him there is no COVID discount."

In Voller's opinion, Havertz is on course to be better than some illustrious Leverkusen alumni.

"For me, he's the best I've seen at Leverkusen, and I've been here for a lifetime. We had Emerson, [Michael] Ballack, Ze Roberto, [Toni] Kroos, but he's on top," Voller added.

Former Germany star Voller said Havertz reminds him of Ballack and Mesut Ozil, adding: "He takes the best bits from both of them."

Voller also has no doubt Havertz will continue to represent Leverkusen for the completion of its UEFA Europa League campaign, with a quarter-final tie against Inter Milan next up.

Timo Werner opted not to play for RB Leipzig in the remainder of the UEFA Champions League after agreeing to join Chelsea, but Havertz did feature for Leverkusen in the second leg of its Round of 16 tie against Rangers and Voller is sure he will do so as long as the team is in the competition.

"Of course he will play [in the UEFA Europa League quarter-final], also because he wants to," Voller said. "I am a bit old-fashioned: for me a season is over when it all ends.

"Nobody leaves first. Now, with COVID-19, there have been transfers before the end of the season, but not from us."