The United striker has started the season like a train, failing to score in only one of his 12 appearances for club and country to date.
"Romelu Lukaku underwent an MRI scan, but no fracture or structural damage has been diagnosed", said an official statement.
Belgium have already booked their place at next summer's World Cup in Russian Federation.
Lukaku featured for United against Crystal Palace at the weekend despite sustaining a knock to his ankle in training.
The striker has sat out of training for the last three days with the injury.More news: Tesco reports 27% profits increase
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Lukaku has been a revelation since swapping Merseyside for Manchester in a stunning £75m deal earlier in the summer and has lifted United to second place on the league table, with only goals giving Manchester City the summit of the log.
"He is very uncertain for Saturday, we will make a decision on Friday".
The Belgian coach stressed that his people are in constant touch with Manchester United's medical team regarding Lukaku and he is keen to remain patient with the player's recovery. "We will give him as long as he can".
He has scored 11 goals in his first 10 games following his £75 million move from Everton in the summer.
Lukaku has been key to Belgium's qualification for next year's tournament Russian Federation, scoring 10 goals in seven appearances.