Lukaku is reportedly ready to accept an offer from Inter's rivals Juventus, snubbing the club where he spent last season on loan.
The 30-year-old is back at parent club Chelsea, where he is surplus to requirements.
Lukaku spent two fruitful seasons with Inter before joining Chelsea in the summer of 2021, only to return to the club on loan last season, scoring 14 goals in 37 appearances.
Inter were looking to do a deal with Chelsea to sign Lukaku permanently but the former Manchester United striker ready to accept a better offer from Juventus.
Inter's ultras released a statement on Tuesday and likened Lukaku to Brutus, one of the conspirators for the assassination of the ancient Roman general Julius Caesar.
“Who betrayed you once will do it again, not because he enjoys it, but because it’s part of his nature,” they said.
“Romelu, you betrayed us all,” continued Inter ultras.
“We defended you during your difficult moment, we helped you when the fans of the team that has been looking for you [Juventus] offended you. Now you repay us with a stabbing worthy of Brutus.
“You kissed that badge worth more than our life to us and now, like any vile mercenary, you sell yourself to the best bidder. One has to be a man before being a champion and you are not as such.
“Farewell, Villain.”
Lukaku has had issues with Juventus fans in the past, especially in the Coppa Italia semi-final first leg last season when he was racially abused by a section of the home fans after scoring a late penalty.
