Lukaku left United to join Inter in August in an €80 million (£74m/$90m) move after falling out of favour under coach Ole Gunnar Solskjaer.
The Chile global forward posted a good luck message and photo to his soon-to-be former colleagues on his Instagram on Thursday afternoon.
The Belgian was subject to criticism on the way out, with former United player Neville tweeting Lukaku, having admitted to being overweight "will score goals and do well at Inter Milan but unprofessionalism is contagious!"
The Norwegian has just Anthony Martial, who will miss today's trip to Southampton through injury, Marcus Rashford and 17-year-old Mason Greenwood to count on between now and January. I am not going to sit here and react in a negative way.
"We just need players that want to play for the club".
United are now seventh in the Premier League table, having taken five points from their first four matches of the season.
Lebanese bank sanctioned by USA denies doing banking activities for Hezbollah
He also said that Hezbollah has entered a new phase of confrontation with Israel. "Iran and Hezbollah are endangering Lebanon", he said.
United will still pay a large chunk of the Chilean's reported £400,000 a week wages so keen were they to cut their losses on a disastrous signing.
"I know him (Sanchez)". I have a special affection for him as a player, of course, but especially as a human being.
"As I said on the way back from tour, we were still looking for one replacement for Romelu if he went,"We are one down to be fair, but we didn't just find the right one".
"He's an incredible, humble guy and a fighter".
"Because I think the way Inter plays, it suits him perfectly".
"But I can not always look back and say this and this and this happened and Ole was not the right manager for me". This is a loan for a year, Chris Smalling's Roma deal is a loan for a year. I could not guarantee him that here.
The United manager said on Friday that he would ideally have been able to bring in a new striking option during the summer transfer window, but the club were unable to get the target they had identified.