The £75 million striker was forced to sit out a meeting with Bosnia-Herzegovina on Saturday as he nursed an ankle complaint.
With a crucial domestic fixture against Liverpool approaching, United boss Jose Mourinho would have been hoping for a positive update on the 24-year-old.
He has now got one, but has also seen Belgium coach Roberto Martinez suggest that he could be used against Cyprus on Tuesday.
The former Everton manager told reporters: “Romelu Lukaku is fit. We are in touch with Man United’s medical team. I haven’t received a phone call from Jose Mourinho as yet.”
While they have nursed one United star back to fitness, Belgium have seen another laid low while away on international duty.
Marouane Fellaini lasted just 29 minutes against Bosnia before being forced off with a knee complaint.
An untimely knock has seen him ruled out of a crunch clash with Liverpool on Saturday, as he joins Paul Pogba on the Old Trafford injury list.
Belgium announced shortly after seeing Fellaini laid low that he was facing “a couple of weeks” out, with his setback coming at a bad time for United.
Despite limiting Mourinho’s options, Martinez remains confident that “unfortunate” injuries will not lead to a breakdown in the relationship between club and country.
He added: “It was a very unfortunate injury for Marouane Fellaini.
“I don’t think the state of the pitch played any part and it was just a collision between two strong players who wanted to win the ball, and unfortunately Marouane ended up with damage in his ligament.
“But there was nothing wrong in that respect so the relationship is very, very good with Manchester United as you would expect.”
With Fellaini set to sit out United’s trip to Anfield, Mourinho is likely to turn to the club’s reigning Player of the Year, Ander Herrera, to help provide cover in the middle of the park.