Shakhtar Donetsk chief executive Sergei Palkin has revealed that Manchester United were working on a deal to sign Fred since April under the specific orders of Jose Mourinho.
However, the £52 million midfielder was pictured yesterday with his ankle on ice and the severity of the injury he has suffered is so far unknown.
A scan may be required as Brazil and team doctor Rodrigo Lasmar monitor Fred ahead of Sunday's final World Cup warm-up match against Austria.
There was better news for Brazil, however, as star forward Neymar was added to coach Tite's main formation on Thursday.
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But Fred's place at the World Cup could be in doubt after he went down hurt during Thursday's session.
Brazil will face their last friendly of the season against Austria On Sunday before traveling to the World Cup in Russian Federation. He sat out training on Friday - Brazil's last session in London before they fly to Vienna - to work alone with medical staff.
But Neymar returned to form in fine style last week, scoring at Anfield after coming off the bench against Croatia.
Brazil kick off their World Cup campaign against Switzerland on Sunday night, before facing Costa Rica and Serbia over the course of June in what is a noticeably competitive Group E.