As well as the weekend's tie, Casemiro will also be out for the midweek home match against Copenhagen in the Champions League because he is suspended.
"Casemiro was absent [from training], having remained in Brazil, on the club’s advice, to recover as swiftly as possible from a small issue picked up while playing for his country," an update on the club's website read.
"He will be unavailable for Saturday’s game with the Blades but is expected back at Carrington early next week to resume training, although he is suspended for the UEFA Champions League encounter with FC Copenhagen at Old Trafford, after being sent off in the defeat to Galatasaray."