"I remember one of my first Champions League games against Slavia Prague when I played really bad - like I was trash that day - and I really got it from him in front of the whole team," Lukaku told an interview with Sky Sports. "It had never really happened to me. It had never happened.
"[He was] telling me that I was really trash and that he would take me off after five minutes if I would have done it again."
Despite the verbal abuse he received from the former Blues boss, Lukaku admits it's taken his game to new heights.
"We played the Milan derby just after that, and I played one of my best games of the season.
"He just gave me that - he stepped on my confidence but it woke me up at the same time. He does it to everybody, it doesn't matter who you are. Everybody is equal."
Lukaku has scored 18 goals in 26 games across all competitions for the Nerazzurri this season.