Lukaku has not enjoyed his second spell at Inter Milan after joining on loan from Chelsea in the summer as he has struggled with injuries this term.
The 29-year-old has only played five times and scored two goals in all competitions for Inter due to a thigh problem.
After more than a month out, the Belgium international made a goalscoring return to action against Viktoria Plzen in the Champions League last month but featured for just 23 minutes in Inter's next game against Sampdoria before getting sidelined again.
Lukaku is not part of the Inter squad travelling to face Juventus in Serie A on Sunday and Inzaghi has confirmed that the former Manchester United striker will only return to club action after the break for the World Cup.
Speaking ahead of the Derby d'Italia, Inzaghi said: "We will be without him, without [Danilo] D'Ambrosio and with [Alessandro] Bastoni to evaluate because he had a fever.
"It is normal for a coach to want to have all his weapons, but we know that playing so much there are difficulties in organising with all the team.
"Lukaku will do another test next week; unlike last time, I can say that I don't think he will be there for the last game.
"I'm sorry, because he worked so hard to be there. We will wait for him after the break, because we know he can give us a great hand."
Nonetheless, Lukaku is still expected to be included in the Belgium squad for the World Cup which kicks off in two weeks time.
