The Manchester United striker had positive results from tests on his ankle injury this week, but is yet to re-join full training with the squad.
Belgium are already assured of winning Group H, meaning there is little to gain in risking Lukaku, with Martinez leaning in the direction of leaving him out ahead of Saturday's game away to Bosnia-Herzegovina.
However, Lukaku — who already has 11 goals to his name at club level this season — is a likely participant in the home match against Cyprus on October 10.
"At the moment, Romelu is working separately," Martinez told reporters.
"He has not joined the group yet since he arrived. We need to be a little bit patient.
"I would say he is very uncertain for Saturday. We will make a decision probably on Friday, but I would say that it is a little bit difficult for him to be involved on Saturday.
"But we are still hopeful he will be involved on Tuesday [against Cyprus]."
Lukaku, though, is not giving up in the battle to be fit for the match in Sarajevo.
Martinez continued: "He wants to play. He came with a little bit of a sore ankle. It is important that he gets that fully recovered. It is a period of the season that is really busy.
"We will give it as long as we can to make the final call but he is very uncertain for Saturday."
Lukaku has been key to Belgium's qualification for next year's tournament Russia, scoring 10 goals in seven appearances.