Lukaku has been receiving treatment at home in Belgium for a hip injury and has ignored calls from Napoli to return to Italy over the past week.
On Monday (March 31), after victory over AC Milan, the reigning Italian champions publicly expressed their annoyance with their Belgian striker's decision to remain home.
Although the 32-year-old attempted to defuse the controversy on Instagram, stating that he could "never turn his back on Naples," his absence from team training has not gone down well with the club's management.
As a reminder, the striker has only played 64 minutes since returning from injury in January.
Napoli's sporting director, Giovanni Manna, has now made a very firm statement to DAZN, announcing planned sanctions for the Belgium international: "Romelu has decided to stay in Belgium to train and recover from his injury. We are not happy, as we would have liked to speak with him here in Naples.
"He is expected to return next (this) week, and he knows there will be consequences."
The striker's return to Campania this week promises to be particularly tense.