Defenders Harry Maguire and Luke Shaw were not involved in Manchester United's training session on Tuesday on the eve of their Champions League group game against Villarreal, the club said.
Maguire and Shaw were both substituted after picking up injuries in the 1-0 Premier League loss to Aston Villa at Old Trafford on Saturday.
Forward Marcus Rashford trained away from the main group, as he continues his recovery from a shoulder injury, along with winger Amad Diallo who sustained a thigh injury in training.
United host Villarreal on Wednesday in a repeat of last season's Europa League final, which the Spanish club won 11-10 on penalties.
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