Barcelona forward Raphinha was substituted in the first half of Brazil's win over Haiti on Monday in Philadelphia, with an injury to his right leg.
The winger received attention from Brazil's medical on the field before exiting the match. He looked visibly upset and was seen getting words of encouragement from teammate Gabriel Magalhães.
"Raphinha felt pain in his right hamstring during the first half of the match against Haiti," the Brazil federation said in a statement after the match. "The player has begun treatment and will be re-evaluated. We will provide updates as soon as more information becomes available."
After the game, Rapnhinha's teammate Vinicius Junior said: "It's a shame that Rapha had to leave the game due to an injury. I think it's the same one he had last time. I hope it's not serious so he can stay with us."
Vinicius was referring to a hamstring injury Raphinha sustained at the end of March while playing for Barcelona that kept him sidelined for a month.
AFC Bournemouth teenager Rayan came on in place of Raphinha as Brazil went on to win the game 3-0 and take top spot in the group after drawing their first match against Morocco.
"We will evaluate Raphinha tomorrow," manager Carlo Ancelotti said after the game. "Right now we're not sure what happened.
"[I put Rayan in the game because] he has good qualities and he has a different profile than Raphinha. In the end, it's small details that determine who comes on and who doesn't."
Brazil is also dealing with an ongoing injury issue to Neymar, who was not included in the matchday squad for the second straight game as he continues to rehabilitate a knock to his right calf.
"Neymar will train tomorrow on his own and then we'll integrate him in the team and he will be available for Scotland," Ancelotti added.
ESPN's Gab Marcotti contributed to this report.