The 21-year-old is set to continue lining up for his current club in August while the Blues move in on their target
Havertz, 21, has won rave reviews for his performances across the interrupted 2019-20 season, scoring 12 goals in 30 games to steer Bayer to fifth place in the Bundesliga.
Goal revealed on Tuesday that the Blues are preparing a formal bid after learning that he favours a move to London, with the aim of pushing down Leverkusen’s asking price of €100m (£90m/$111m).
Any deal, however, will have to wait until Leverkusen’s European adventure is over.
“It is set in stone,” Voller fired when asked by Kicker whether Havertz would line up for the club in the Europa League. “There is no new stance.”
Bayer resume their Europa League campaign on August 6, when they host Rangers in the second leg of the clubs’ last-16 tie holding a 3-1 aggregate advantage from the opener.
While Chelsea believe the financial impact of the coronavirus pandemic may prompt Leverkusen to accept a lower bid for Havertz, Voller is adamant the Londoners will have to pay market value.
“There will be no corona bonus,” he added, before admitting: “No matter who the player is, this is a special transfer window.”
And despite that considerable outlay manager Frank Lampard is open to further new faces, with Atletico Madrid goalkeeper Jan Oblak joining Havertz at the top of the club’s reported wishlist.
“We’ll see. I can’t answer that one, we’re not there yet,” Lampard told reporters in July when asked about potential recruits in the transfer window.
“We have to focus on what’s in front of us and we’ll see. I wouldn’t want to compare it to any other spending summer, we’ll see how I feel and we feel as a club and if the squad needs strengthening or the balance needs changing.
“If it does and we make moves, great. At the moment we don’t know.”