The development came amid reports the talented midfielder is on the verge of completing a transfer to Chelsea.
Frank Lampard is said to be determined to add more depth within his ranks after landing four other major signings including Timo Werner and Hakim Ziyech.
It is believed the Blues have already set their sights on Havertz before wrapping up their summer business.
Havertz has already reportedly agreed a five-year contract at Stamford Bridge, with Chelsea in line to cough a staggering £72million to land the forward.
The player’s recent absence from Leverkusen’s pre-season further fuelled speculation he could be headed of the exits.
His manager Bosz has now come out to confirm Havertz will not be returning to Leverkusen after with German national team.
“I don’t expect Volland (set to join Monaco) and (Kai) Havertz to train with us again,” Metro UK quoted Bosz saying.
“It’s possible more players will transfer and we definitely still have to add some players,” he continued.
The 21-year-old midfielder has been linked with a move to Stamford Bridge all summer long as the Blues continued to beef up their squad for competition next campaign.
Having already signed off Timo Werner and Hakim Ziyech, Frank Lampard is not satisfied with his set up for the 2020-21 season.
SunSport reports that the West London club has now been given the green light to finalise his deal after Roman Abramovich released a sum of £150 million for the move.