DOHA - Brazil were sweating on the fitness of Neymar on Friday after their talisman sprained his ankle in the World Cup win over Serbia.
The forward suffered the injury in a collision with Nikola Milenkovic during the second half of the 2-0 win in Qatar on Thursday in Brazil's opening match.
The 30-year-old Paris Saint-Germain player attempted to continue but was substituted with about 10 minutes to go, shortly after Richarlison put Brazil two goals ahead.
Neymar was seen limping heavily after the game in Doha and photos showed swelling on his right ankle.
He declined to speak to journalists as he left the stadium, but posted a light-hearted message on Twitter, without making reference to his injury.
"Tough game but it was important to win," he said. "Congratulations team, first step taken... six to go."
Team doctor Rodrigo Lasmar said it was too early to jump to conclusions.
"We need to wait 24 to 48 hours to have a better assessment," said Lasmar. "We have not scheduled any MRI (scan) and tomorrow we'll have a new assessment.
"We need to wait, we cannot make any premature comments about his evolution."
Coach Tite was optimistic that Neymar would be back to lead Brazil's bid for a record-extending sixth World Cup crown.
They next face Switzerland on Monday, with their final Group G match against Cameroon.
"You can be certain that Neymar is going to play in the World Cup," Tite said, adding that the attacker had initially stayed on the pitch after hurting his ankle "because the team needed him".