I doubt with Milan has enough money for signing Lukaku due should fight with Saudi Pro League team give bid for buying Lukaku from Chelsea, its seems dilemma for Lukaku position right now, he has denied for playing with Saudi Pro League teams but his previous team Chelsea want to sell him there. Right now the future from Lukaku depend on Inter Milan want to pay higher fees transfer for Chelsea or Lukaku will return back as loan option from Inter Milan. Inter should keep him stay for one year later after leaving by Edin Dzeko, Inter's attacking line only left Lutaro Martinez right now.
For Lukaku performance in this season not really bad, he has success bring Inter lead to final stage in Champion League but he got injured and absent on many game for Inter Milan.
I don't think Lukaku will be considered as important for Milan after he was important for rival club Inter. I don't think Milan will really wants to sign Lukaku from Chelsea as striker, even if they have the money to complete a transfer. Lukaku also doesn't seem to suit Milan's style of play, he would rather be at Inter for a long time after he was known as a dangerous striker at Inter for several seasons.
Even if Chelsea have to sell him, it is very likely that Lukaku will not be sold to Milan. There are a lot of better players than Lukaku, so Milan shouldn't be too interested in signing Lukaku.