Romelu Lukaku has been sent for an MRI scan on a foot injury, the Belgium national team have confirmed.
Manchester United striker Lukaku was called up to Roberto Martinez's squad for the opening qualifiers of their Euro 2020 qualifying campaign, but missed training on Monday.
And Belgium confirmed on Twitter that the 25-year-old, who has scored 45 goals in 79 international appearances, has had a scan to determine the extent of the problem.
The Red Devils kick-off Group I with a home match against Russia at the King Baudouin Stadium in Brussels on Thursday, before travelling to face Cyprus in Nicosia on Sunday.
Should Lukaku not be fit, Martinez has Dries Mertens, Christian Benteke, Divock Origi and Michy Batshuayi as alternative striking options.
Former Tottenham midfielder Mousa Dembele and Paris Saint-Germain defender Thomas Meunier have both pulled out of Belgium's squad due to injury.