Standard Sport understands that Frank Lampard hopes to seal a £70million deal for the German international following Leverkusen's exit from the Europa League quarter-finals at the hands of Inter Milan.
Havertz was on the scoresheet during the last-eight clash in Dusseldorf on Monday night, but goals from Nicolo Barella and Romelu Lukaku condemned Peter Bosz's side to an exit from European football's secondary club competition.
Chelsea - having already significantly boosted their attack this summer with the signings of Hakim Ziyech and Timo Werner - are now looking to seal a quick deal for Havertz in order to give him sufficient time to settle in west London ahead of the start of the 2020/21 Premier League season on September 12.
However, Voller claims an exit will only happen this summer if Leverkusen's expectations are met in full.
"No decision has been made yet. I'd like to repeat myself by emphasising that we're talking about a wonderful footballer,' he told German publication Kicker.
"There is nothing new in this regard. We have a clear and mutual agreement with him and his representatives that he can only leave under certain conditions.
"Otherwise he will stay."