Brazil winger Neymar suffered a sprained ankle during his team's victory over Serbia at the World Cup.
Neymar was substituted in the 80th minute and looked emotional on the bench as he watched his team see out a 2-0 victory.
Brazil's team doctor Rodrigo Lasmar says that it will be 24-48 hours before the severity of the injury can be determined.
A picture of Neymar with his boot off showed severe swelling on his ankle.
The 30-year-old was injured following a challenge from Serbia defender Nikola Milenkovic.
Brazil won their opening group game courtesy of a brace from Richarlison.
However, despite the fact that they have an array of star at their disposal, losing Neymar would be a significant blow for Tite's side.
Brazil's next fixture is against Switzerland on Monday before they take on Cameroon four days later.
Neymar will be assessed to determine whether he will be able to be involved in the upcoming games.
Now competing at his third World Cup, Neymar is determined to win the famous trophy.
With 75 goals for his country, Neymar is just two behind Pele's record goalscoring tally for Brazil. In addition, he has over 100 caps for Brazil.
After a goalless first half against Serbia, Brazil took the lead in the 62nd minute as Richarlison scored after Vinicius Junior's effort was saved.
Richarlison proceeded to make it 2-0 with an acrobatic finish.