Team doctor Rodrigo Lasmar had this to say on the midfielder's status.
Manchester United announced that they had agreed a deal to bring the Shakhtar Donetsk midfielder to Old Trafford as they began their summer recruitment drive.
United €56m man Fred has apparently suffered ankle trauma just one week out from this year's World Cup in Russian Federation. "Tomorrow we will know whether he will have to be further examined or not".
Fred has made eight appearances for Brazil and made head coach Tite's final 23-man squad for the World Cup in Russian Federation.
The Paris-Saint Germain man came off the bench to score in Brazil's 2-0 win over Croatia on Sunday for his first goal since February.
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The man has won Ballon d'Or five times, led Portugal to win the Euro cup in 2016, and is Real Madrid's talisman. Cristiano Ronaldo has been with the Madrid club since 2009.
However, Fred has remained with the Brazil squad and looks set to take part in the World Cup in some capacity.
Brazil talisman Neymar is the most probable replacement for Fred in midfield against Austria in Vienna but the South American's will be sweating on Fred's fitness as he has improved tremendously over the past few seasons.
"Everyone wants to fight for a position, our trainings are very strong, " left-back Marcelo said.
Brazil - led by head coach Tite - will face Switzerland (June 17), Costa Rica (June 22) and Serbia (June 27) in Group E at the World Cup in Russian Federation. He had a medical on Monday and returned to training with the Brazil national team the following day.