Lukaku was absent for Belgium during the international break and also missed Everton's win over Southampton at the weekend due to a hamstring problem.
The striker may be in the reckoning for this weekend's Premier League match, although team-mate Gibson is set to miss the remainder of the season after fracturing a metatarsal.
"With Darron Gibson we had fantastic news from the specialist because the fracture he has doesn't need surgery," manager Martinez told Everton official website.
"Hopefully he will be back sooner rather than later but I think it will be difficult for Darron to play again this season, but it is something we aren't certain over.
"Romelu Lukaku has had two very good sessions but [Tuesday] was too early for him to be involved with the group.
"He has got his own one-to-one programme and we are very pleased with his situation at the moment.
"I am quite confident he could make the squad for Swansea but if he doesn't he will be back for the Burnley game."
