The former Everton boss acknowledged that it would be "difficult" for Lukaku to be fit in time for Saturday's game, but he remains hopeful that the striker could be back fit for the visit of Cyprus on Tuesday.
Lukaku has been in fine form since joining Manchester United from Everton in the summer, scoring 11 goals in 10 games in all competition since his big-money move.
However, the 24-year-old injured his ankle during the 4-0 victory over Crystal Palace on Saturday and is facing a race against time to be fit for international duty.
Speaking to the press on Wednesday, Martinez said: "At the moment, Romelu is working separately.
"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."