New Manchester United Fred has suffered a "trauma in his ankle" and will be examined in the next 24 hours.
Brazil team doctor Rodrigo Lasmar says the midfielder will undergo further tests to understand how serious the injury is.
The Red Devils have agreed a £47million deal for the 25-year-old.
The former Shakhtar Donetsk man was Jose Mourinho's first summer signing.
"Today Fred had trauma in his ankle but it is too early to say anything about it," Lasmar said.
"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."
