Brazil team doctor Rodrigo Lasmar has revealed that Fred suffered 'trauma' to his ankle during training on Thursday.
Fred - who has just agreed a deal to sign for Manchester United - has been named in Brazil's squad for the World Cup, but the 25-year-old appears to be a doubt for the tournament.
The midfielder was pictured receiving treatment after a challenge from Casemiro, and Lasmar has suggested that Fred and Brazil must wait before making an assessment over the knock.
Lasmar is quoted as saying by The Independent: "Today Fred had trauma in his ankle but it is too early to say anything about it.
"Tomorrow we watch to see what happens and then decide if we need to do any exams or not, but at the moment it is too early to say anything about him."
Brazil's first match in Russia is against Switzerland on June 17.
