The 25-year-old's four goals leave him behind only England forward Harry Kane (five) in the Golden Boot race.
And Sanchez, whose Chile failed to qualify for Russia 2018, hopes to see Lukaku finish the tournament as the top scorer.
"Lukaku is fine, on fire. He has four goals," he said at a sponsorship event Friday.
"I hope he is the top goalscorer of the World Cup."
Lukaku sat out the Group G finale against England due to an ankle injury, but Roberto Martinez says that he, along with Vincent Kompany and Thomas Vermaelen are all fully fit and available for selection.