Kevin de Bruyne and Eden Hazard were replaced in the second half of Belgium's 1-0 win over Portugal in the European Championships round of 16 on Sunday.
De Bruyne was asked to replace due to injury after a back tackle by Portugal's Joao Palinha earlier in the game. He limped a bit and slowly walked out of the field.
De Bruyne sat down and shook his head, pointing to his left ankle. He seemed fine after being injured the first time during the first half, but could not continue after only two minutes into the second half.
Dries Mertens entered the match in place of De Bruyne.
The Belgian's injury issues worsened minutes from full-time when Hazard was sidelined with a hamstring injury after pulling out of a challenge and asking for a sub at the near touchline.
"We will now take 48 hours to assess the condition of both players. We will now go back to Belgium and have their injuries scanned tomorrow," Belgian boss Roberto Martinez told a post-match news conference.
"It's too early to say how they're doing. With Kevin, it's the ankle - he really couldn't turn in the second half. With Eden it's muscle, but we'll have to wait for a diagnosis."
Both players were injured before the start of the tournament, but have recovered well to help Belgium top their group and remain vital to the team's hopes of progressing to Euro 2020.
Belgium will next face Italy in the quarter-finals on Friday, July 2.