Reports suggest Neymar was in tears on the bench and he did not celebrate his team’s victory, instead heading straight down the tunnel with his boot off and his swollen foot still on show.
The national team doctor Rodrigo Lasmar said the Brazilian superstar suffered the injury after a collision with his opponent.
Neymar failed to complete 90 minutes as he was substituted in the 79th minute as he limped off the field late in the second half.
The subject of nine fouls, Neymar was visibly distraught as he left the pitch and was seen speaking with team doctors, who were applying ice to his clearly swollen ankle.
“We need to wait 24 to 48 hours to have a better assessment,” Lasmar said. “We have not scheduled any MRI and tomorrow we’ll have a new assessment.
“We need to wait, we cannot make any premature comments about his evolution.”
Neymar was seen limping heavily after the game while photos of the striker showed swelling on his right ankle.
Coach Tite said the Paris Saint-Germain player initially stayed on the field after hurting his ankle “because the team needed him”.
He also moved to play down fears that the 30-year-old could face a lay-off long enough to end his World Cup campaign.
“You can be certain that Neymar is going to play in the World Cup,” he said.
A downcast-looking Neymar declined to speak to journalists as he left the stadium on Thursday.