Luke Shaw and Harry Maguire were not involved in Manchester United's training session on the eve of their second Champions League group stage match against Villarreal.
Shaw and Maguire were both forced off in the 1-0 Premier League defeat to Aston Villa on Saturday and seem set to miss the Villarreal tie. Shaw is believed to have been unwell on the morning of the game.
If both of them are absent, United would be without three of their first choice defenders as Aaron Wan-Bissaka is suspended following his red card against Young Boys.
Diogo Dalot is expected to come in at right-back and Victor Lindelof is in line to partner Raphael Varane, who is due to speak at the pre-match press conference.
Alex Telles could replace Shaw at left-back, despite his disastrous performance in the League Cup loss to West Ham last week.
Marcus Rashford and Amad continued their light training sessions away from the United squad at their Carrington training complex on Tuesday morning.
