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 withdrew from Belgium's squad last week 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.

"Romelu Lukaku did not respond to today's call-up for the resumption of training," Napoli said in a statement.

"The club reserves the right to decide whether to take appropriate disciplinary action, as well as whether to continue the player's activity with the squad on a permanent basis."

BBC Sport has contacted Lukaku's representatives for a response.

Lukaku has played just 64 minutes of football this season.

The ex-Inter Milan forward has 124 caps for his country and is aiming to feature at a fourth World Cup this summer.

Belgium's all-time leading scorer, with 89 goals, said on Monday that he "could never turn his back on Napoli" and that he wants nothing more than to "play and make my team win".

Lukaku, whose father Roger died in September, said: "This season has been very challenging for me, between the injury and personal loss.

"I know there has been a lot of noise over the last few days about my situation and it is important to clarify everything.

"The truth is that in recent weeks I didn't feel well physically, I underwent some checks while I was in Belgium and it turned out there was inflammation and fluid in the iliopsoas muscle, near the scar tissue.

"It is the second problem I have had since I returned at the beginning of November. I chose to do the rehabilitation in Belgium so that I can be ready when called upon."