Lukaku joined Napoli from Chelsea in 2024
Romelu Lukaku could face disciplinary action after Napoli claimed the striker ignored a request to attend training.
The 32-year-old has missed a large chunk of the season with a hamstring injury and has yet to start a game.
Lukaku last week withdrew from Belgium's squad for internationals against the USA and Mexico, opting instead to focus on his fitness.
Napoli expected him to return to Italy, but they say the former Chelsea, Everton and Manchester United player did not report for training on Tuesday.
