The Belgium striker, 26, was also called “overweight” by the former Manchester United defender on Twitter.
Lukaku left the Old Trafford club this summer to join Serie A side Inter Milan for £74m on a five-year deal.
“Don’t question my professionalism,” Lukaku told BBC Sport. “I live for this game. I am at home all the time. I try to do everything to improve.”
In a wide-ranging interview with BBC Sport’s Simon Stone in Milan, Lukaku spoke about:
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