The midfielder, who cost £72million to sign from the Bundesliga side, has struggled to make an impact at the London side.
Speaking to VI, the 57-year-old Bosz said: “Havertz's greatest quality lies in the opponent's box.
“Then Havertz does not get enough into the penalty area."
But the forward has faced struggles of his own, picking up a knee injury in pre-season and scoring just two goals in 14 appearances.
The situation at Stamford Bridge has seen reports emerge that Havertz is privately regretting his decision to leave Leverkusen.