Martinez chose to bring Lukaku off the bench after 66 minutes on Tuesday night with Belgium already qualified for Russian Federation and winning 3-0 - despite the striker having just recovered from an ankle injury.
The 29-year-old has returned to Carrington to undergo further assessment with the United medial team and it's not yet clear exactly how long the midfielder will be on the sidelines for.
But the Manchester United boss isn't anxious because he insists he has adequate cover in his squad. I don't know. But we are better'.
"From what I read I don't think he can play the match". With Martinez declaring that Lukaku is a 100 percent fit to start, Mourinho will certainly hope that the injury gods don't conspire against him with Marouane Fellaini out for 3 weeks with a knee injury.
The Red Devils are now second in the Premier League table and level on points with leaders Manchester City heading into their crunch clash with Liverpool this weekend.
Jose Mourinho has dismissed the suggestion that Romelu Lukaku and Marouane Fellaini's injury concerns will have an impact on Manchester United's clash with Liverpool. "But last season we did not beat West Ham or Everton at home or Southampton away, so we are already six points better off". If they respect me as much as I respect them, we are going to have another one of those matches.
Mourinho and Lukaku have been reunited to devastating effect this season, with the £75m striker spearheading Manchester United's attack and scoring 11 goals in his first 10 appearances.
He's become an important part of Mourinho's plans, but the Portuguese isn't anxious about players missing through injury.