Neymar was forced off just minutes into Tuesday's friendly match with Cameroon due to an apparent thigh injury.
The Paris Saint-Germain star was captaining the Selecao in the clash at Stadium MK, but pulled up injured while playing a cross in the game's early moments.
Neymar's day lasted just eight minutes, as he was removed from the match with Everton star Richarlison taking to the field in his place while Marquinhos assumed captain's duties.
Neymar was treated by Brazil's physio team in the dressing room for a groin injury, although the severity of the injury is not yet known.
"He felt a discomfort on the right side of his groin region," Brazil doctor Rodrigo Lasmar told Globo after the match . " He complained and underwent an early assessment, but he already began his treatment. It doesn't seem serious at first, but we should wait and see how he develops."
The winger was playing his second match in four days after taking in 90 minutes and scoring the lone goal from the penalty spot in Brazil's 1-0 win over Uruguay.
Manger Tite had recently praised the his adjustment to the captaincy, saying that he has grown into a calming presence within the Selecao side.
Brazil are in England for the pair of friendlies, having played Uruguay at the Emirates Stadium before taking on Cameroon at Stadium MK in the team's final two matches of 2018.
Neymar's injury could prove a major blow for PSG, who are currently in a tight situation in Champions League play.
The French powerhouse currently sits third in their Champions League pool with matches against the Reds and Red Star Belgrade remaining to close the group stage.
PSG have amassed five points from four games with both Liverpool and Napoli currently on six.
Neymar has started 16 matches in all competitions for PSG this season, scoring 10 league goals while providing five assists.
The Brazilian trails only Kylian Mbappe on the team's goalscoring charts as the Frenchman has scored 11 times this campaign.