Lukaku is due to return to Napoli on Monday, Italian daily Quotidiano Sportivo reported, after spending five weeks in Belgium recovering from persistent injuries.
The 32-year-old was fined by Napoli after he failed to rejoin the club following the March international break, opting instead to remain in Belgium to continue treatment with his preferred physiotherapist.
Lukaku had joined up with Belgium’s squad ahead of a pair of World Cup warm-up fixtures but did not travel because of hamstring and hip complaints.
Napoli docked him 20% of his monthly salary, reports said, after he failed to return, although he went back on April 20 and was granted permission to continue his treatment in Belgium.
He did not speak to coach Antonio Conte, who voiced his disappointment in a television interview four days later.
“I didn't have a chance to talk to him,” Conte said. "I know that one of our directors did.
"Lukaku came to the training centre. My office is there, but no one knocked on my door. That really hurt me. I expected a greeting, a message or something like that.
"In these kinds of situations, the coach tries to understand everyone, but no one really makes an effort to understand the coach. I hadn't expected this situation.”
Second-placed Napoli have three Serie A fixtures remaining this season. They host Bologna and Udinese with an away trip to Pisa in between.
Lukaku, who turns 33 later this month, has not started for Napoli this season, making six substitute appearances and netting a goal at Verona in February.
For Belgium, he has scored 89 times but won the last of his 124 caps in the 4-3 home win over Wales in World Cup qualification last June.
Belgium play against Egypt, Iran and New Zealand in Group G at the World Cup.
