Neymar hobbled out of a training session on Tuesday, setting alarm bells ringing in the Brazil camp as they prepare for their second World Cup group game against Costa Rica on Friday.
"Neymar came out of training today with a painful right ankle," said Vinicius Rodrigues, a spokesman for the Brazilian Football Confederation (CBF).
He put the the knock down to the number of fouls Neymar received in Sunday's 1-1 draw against Switzerland in Brazil's opening Group E outing.
The 26-year-old could be seen grimacing as he held his right ankle after feeling pain as he took part in a light session for those who had started that game.
Neymar had not taken part in training on Monday, as the side returned to their base in Sochi on Russia's Black Sea coast.
Rodrigues confirmed the problem concerned the PSG star's ankle and not the foot he fractured in February, an injury that required surgery and forced him to miss the rest of the club campaign.
"He will stay there [with the physio] today and tomorrow [Wednesday] morning, and will train as normal tomorrow," added Rodrigues.