The Belgium international posted a topless selfie on social media and added the words: "Not bad for a fat boy."
Journalist Kristof Terreur shared the image and noted his weight at previous clubs Anderlecht, Chelsea and Everton:
Neville had commented about Lukaku's physical condition in a response to a Twitter post from The Athletic's Andy Mitten prior to the striker's departure from Manchester United to Inter Milan:
Meanwhile, BeIN Sports commentator Tancredi Palmeri said that Lukaku would miss Inter's first Serie A game of the season after arriving four kilograms heavier than expected:
Former Manchester United defender Gary Pallister has also remarked on Lukaku's weight when talking to AmericanGambler.com (h/t Alexander Netherton at Eurosport).
"I think Lukaku is a goalscorer and he will score plenty of goals, but the way they want to play at times, he's too heavy," he said.
However, sports journalist Siavoush Fallahi said Lukaku is not out of shape but is carrying too much muscle:
This is not the first time Lukaku has taken to social media to defend himself. He was forced to delete a post revealing training statistics amid claims he lacked pace, per James Ducker at The Telegraph.
Lukaku spent two years at Manchester United after moving from Everton in 2017. He scored 27 goals in all competitions in his first season but managed only 15 in his second.
He has already found the back of the net in Inter colours. He bagged four goals in a 8-0 win over Virtus Bergamo in a pre-season friendly:
The 26-year-old was also on target in a 2-0 pre-season victory over Gozzano:
Inter begin their Serie A campaign on August 26 against newly-promoted Lecce at the San Siro. Much will be expected of the Nerazzurri after bringing in Antonio Conte as manager and signing players such as Lukaku, Valentino Lazaro and Nicolo Barella.