Before giving his squad a day off after Saturday's 5-2 Group G win over Tunisia, the Spaniard waved away talk of supplanting stuttering favourites like Germany or Brazil and acknowledged defensive lapses will have to be tightened against England on Friday morning (Singapore time).
The victory also meant that having trumped Panama and Tunisia, the Belgian team is now on top of Group G, with their final game against England to be held on June 28.
With Belgium eyeing their first run to the final, one worry is a knock to the ankle late in the first half which forced Lukaku off a quarter of an hour into the second.
"I think his role now with the national team has become that".
"Football has got a odd knack of punishing you when you don't treat things professionally", he said.
Experienced performers Thomas Vermaelen, Kompany and Marouane Fellaini have all been left out of the starting XIs so far, while Chelsea striker Michy Batshuayi came off the bench to score - as well as miss a host of chances - against Tunisia.
Chelsea star Eden Hazard suffered a calf injury as his side won comfortably 5-2 against Tunisia in Russian Federation.
Martinez said Lukaku and Hazard, who were withdrawn in the second half, and midfielder Dries Mertens had slight injuries and could be among a series of changes for the England game.
"It's important to finish top of the group, because - psychologically - it could have an influence on our opponent who says to themselves they're going to play against a team that was the best in its group", he said.
"The difficulty that we have in Belgium is that we have too many players that deserve to win the World Cup", he said of the talent he can choose from, at least in some positions. "The whole of Belgium should celebrate". We played much better than we did in the first game.
"The reality is that we have qualified - you are only as good as the 23 players". "And our work will start tomorrow morning".
The towering all-time leading goalscorer for his country (40) could not be stopped, scoring twice to take his tournament tally to four in two games.