Corriere dello Sport says he's weighed in at 104kg and medical staff do not want him to be above 100kg.
However, Lukaku hit back at the suggestion he has piled on the pounds over the summer with a picture on Instagram.
“Not bad for a fat boy," was the caption on his Instagram Stories.
Inter open their season on Monday against Lecce.
Lukaku on his snapchat - he’s really not one for taking criticism without responding pic.twitter.com/g3hEcp3bbn— Full Time DEVILS (@FullTimeDEVILS) August 17, 2019