The Blues are set to pay an initial club record fee of £72m for the 21-year-old midfielder in a deal that will take their summer spending beyond £200m.
Havertz met up with the Germany squad in Stuttgart yesterday but his move to Stamford Bridge is edging closer to completion.
He has agreed personal terms on a five-year contract and, once the deal is finalised, will become Frank Lampard’s seventh summer signing.
Chelsea have already signed Hakim Ziyech, Timo Werner, Ben Chilwell and Thiago Silva, as well as signing Malang Sarr and bringing in teenager Xavier Mbuyamba from Barcelona.
Blues owner Roman Abramovich has sanctioned heavy investment in the team and sent out a signal of intent about Chelsea’s ambitions to become title challengers again.
Lampard hopes the signing of Havertz will help Chelsea close the gap on Liverpool and Manchester City next season and his summer spending will not stop there.
He wants to bring in a top-level goalkeeper after losing faith in Kepa Arrizabalaga and has been linked with a move for Rennes goalkeeper Edouard Mendy. Chelsea have had an opening bid of around £14m rejected but are expected to return with a second bid.
Havertz will provide Chelsea with more options in attack and Lampard will hope he is signed in time for their opening match of the season, against Brighton, on September 14.
Chelsea’s preparations for the new season were thrown into chaos last week after eight players, including Christian Pulisic, Tammy Abraham and Mason Mount, were forced into quarantine.
Without those players, Lampard’s side drew 1-1 with Brighton at the Amex Stadium on Saturday in their first pre-season friendly.
New signing Werner scored on his first appearance, but there was a worrying moment for Lampard when Ziyech limped off.
Lampard described the injury as “a little twist to the knee” and the Morocco winger will be assessed this week.
Havertz is in the Germany squad to face Spain and Switzerland in the Nations League this week. He has scored 46 goals in 150 appearances for Leverkusen but the German club do not expect him to return to training with them after the international break. Leverkusen manager Peter Bosz said: “I do not expect Havertz to train with us again.”