Napoli’s acquisition of Lukaku, 31, has been spearheaded by their boss Antonio Conte, under whose guidance the Belgian flourished during two fruitful campaigns at Inter Milan from 2019 to 2021.
The forward returned to Chelsea in 2021 for £97.5m but has spent the last two seasons on loan in Italy, initially back at Inter and then with Roma.
Lukaku netted 24 league goals as he clinched Serie A under Conte in 2021, his form prompting Chelsea’s decision to bring him back.
Offloading the Belgian – who hasn’t featured for Chelsea since May 2022 – removes his £325,000-a-week wages from the books.
In a pre-match briefing, Conte mentioned Lukaku could make his Napoli bow in Saturday’s clash against Parma (19:45 BST).
Lukaku’s exit coincides with Chelsea midfielder Tino Anjorin’s move to Italy’s Serie A, joining Empoli on a three-year contract.
Chelsea and Saudi Pro League outfit Al-Ahli are both negotiating to sign Nigerian striker Victor Osimhen, 25, which will help Napoli balance their spending.