Brazil team doctor Rodrigo Lasmar said Fred will be monitored, with Tite's men set to play Austria on Sunday in their final friendly before Russian Federation 2018.
Brazil face Austria on Sunday in their final friendly before their World Cup campaign starts against Switzerland in Rostov on June 17 and Globoesporte has reported Fred is expected to miss out.
It is too early to say, we have to see how he develops in the next 24 hours,"Brazil physician Rodrigo Lasmar said when asked for a full diagnosis on Thursday evening".
Lasmar added: "At the moment it is too early to say anything about him".
But Brazil manager Tite expects Fred to be fine to resume training with the national side ahead to the World Cup.
Brazil are now based at Tottenham's training base prior to flying out to Russian Federation, and footage posted to Twitter by Luiz Felipe Castro showss Fred go to ground after a challenge from Real Madrid's Casemiro.
Manchester United this week agreed to sign Fred from Ukraine's Shakhtar Donetsk in a deal that British media have put at some 52 million pounds ($70 million).
"This is the World Cup, everyone is training hard and working hard", said Marcelo.
"But I believe it's not that serious, I believe it's not a big problem for us and I think he'll be back with us as soon as possible".