The striker is doubtful to make the Toffees' match against Swansea City this weekend and Martinez admits that it would be a blow.
He says that there are no like-for-like replacements for Lukaku in Everton's squad and he has suggested that they may look to play football in a slightly different way on Saturday.
"Obviously Romelu is a massive player for us and it will be a worry," he said. "We are going to miss him. But I think in football you can play in different ways.
"The goalscoring threat that Rom brings to the side is unique, and I don't think we have a like for like replacement in that respect. But I think we have got other players that they've shown that they can bring a different way of playing and they can be as effective."
Lukaku has had a fine season, despite Everton's disappointing league campaign, and he has been in brilliant form recently.
The 21-year-old has 18 goals for the campaign, with eight of those strikes coming in his last nine games, and without him the threat that the Toffees pose does seem limited.
Everton have just Arouna Kone in reserve and it is likely that a striker will be on top of Martinez's wishlist this summer.
Lukaku is set to remain the main man on Merseyside, though, and the hope is that with increased service he will be able to achieve an even greater tally next year.