Georginio Wijnaldum suffered a broken leg in training, his new team Roma announced on Sunday.
"Following an injury sustained during training this afternoon, Georginio Wijnaldum subsequently underwent medical tests that confirmed the presence of a fracture to the tibia in his right leg," the Serie A club said in a statement.
Roma did not say for how long the Netherlands midfielder would be out, adding that he will "undergo further assessments in the coming days".
The injury casts doubt over his chances of playing at the coming World Cup in Qatar, which starts in mid-November.
Wijnaldum has won 86 caps for his country, scoring 26 times.
He moved to Roma on loan from Paris Saint-Germain earlier this month and his injury deprives coach Jose Mourinho of a player who had made Roma a potential dark horse for the Serie A title.