Lukaku and Hazard scored twice in Saturday's 5-2 rout of Tunisia before being replaced in the second half, while Mertens also made way with four minutes to go after a typically energetic display.
Martinez was already planning to shake-up his side to face the Three Lions on Thursday with qualification to the last 16 guaranteed if, as expected, England avoid defeat to Panama on Sunday.
The Spaniard said: "If we had seven days to prepare, and then have another seven days after the England game we would carry on with the same team.
"I do believe in international football it's important to have an understanding between the players. The reality is we are qualified and you are only as good as the 23 players. There will be opportunities for other players, we can give minutes to players who deserve to be at the World Cup."
On the injuries, he added: "Lukaku picked up an ankle injury, Hazard picked up a calf injury, and Dries Mertens had a knock on his ankle. We will assess them. There will be major changes against England.
"Romelu has external ankle ligament damage to his left foot. It was a knock he had late in the first half. He tried to play through it, but he couldn't. He did well to last what he lasted. He will be assessed and then we will find out in 48 hours."
Martinez also dismissed suggestions winning Group G may not be beneficial due to the raft of surprise results elsewhere.
Although it remains guesswork at this stage, the pool winners could end up facing the winner of Brazil and Germany in the last eight, while the runners-up may get one of Mexico, Sweden or Switzerland assuming they dispense with the winner of Group H in the last-16.
Going easy against England has not crossed Martinez's mind, though.
He said: "Football has a strange knack of punishing you when you don't treat things professionally.
"What's important for us is that every player who deserves to be on the field will have a role to play. We need to approach the game with England really well, we shouldn't be thinking of anything else other than preparing the team that will be starting that match."
Despite the emphatic scoreline against Tunisia, Belgium's display was far from perfect and Martinez admitted there was still much work to do.
"We must remember that it was a game that suited our style," he said.
"Give huge credit to Tunisia, they wanted to win from the beginning, they pressed high up, they were happy to leave space and the credit we deserve is that we used that space well.
"We are still growing, we need to do better, we didn't manage the game well enough in moments."
In scoring twice, Lukaku not only joined Cristiano Ronaldo as the leading marksman in the World Cup with four, he also became the first man since Diego Maradona in 1986 to score successive braces at the tournament.
But, as he did on Friday, Martinez played down the importance of individual awards.
"Romelu will try to score as many goals as he can but not at all costs," he said.
"What's important is that we have the right attitude on the pitch that allows you to work well as a team. Rom, like any other player, is aware the only thing that matters is to keep working, to keep getting better as a team and then if you do that well, you will get individual rewards.
"He was incisive, he was in the right position, in a confident mood and in front of goal he was as clinical as you would expect."