Lukaku was pictured in Anderlecht training apparel on Tuesday after deciding to work away from Manchester ahead of a potential move to Inter.
And reports claim that the former Chelsea and Everton star has been fined more than once for his behaviour in recent days, the first for tweeting a copy of United’s sprint stats and the latter for his decision not to return to the club’s Carrington training ground on Tuesday.
This follows suggestions that his relationship with United boss Ole Gunnar Solskjaer has broken down, with the Norwegian having apparently informed Lukaku that he will be expected to train with the Under-23s until there is some resolution regarding his future.
And Goal has been informed by a source close to the negotiations that talks are ongoing to find a deal between United and Inter which would see Lukaku finally link up with Nerazzurri head coach Antonio Conte.
The Italian has sought to sign Lukaku on more than one occasion in the past but has thus far been unsuccessful in his attempts, with him having failed to land the Belgian while in charge of Juventus and Chelsea.
However, following the end of talks between Juve and United relating to a planned swap deal involving the 26-year-old and Paulo Dybala, Inter are now overwhelming favourites to secure the striker’s signature.
The Red Devils ultimately decided against moving forward with talks over Dybala's potential arrival due to the Argentine’s exorbitant financial demands. Christian Eriksen has also been linked with the club but reports suggest that move has also fallen through.
Lukaku arrived at United in the summer of 2017 from Everton for a £75m ($91m) transfer fee and the Reds are looking to make their money back on the No.9.
And with Solskjaer in no rush to seek out a replacement for the forward, United are under no pressure to force a quick exit ahead of Thursday’s English transfer deadline.
The window for Italian clubs to register doesn’t close until September 2, giving Inter more than three weeks to finalise a deal with United regarding the purchase of Lukaku.