It's a soft tissue injury, so it'll probably take a while. We'll see, says manager Ruben Amorim.
Fernandes did not come on for the second half at Villa Park, with it being thought he had pulled a muscle in the back of his thigh.
Injuries are a constant in the intense Premier League football at the moment. Manchester United have several players on the injury list and will also be without the trio of Bryan Mbeumo, Amad Diallo and Noussair Mazraoui, who are participating in the African Championships.
