Harry Maguire and Luke Shaw skipped Manchester United training on Tuesday and are doubts for their side's Champions League group stage match with Villarreal on Wednesday.
The Red Devils defensive duo both hobbled out of Saturday's 1-0 home defeat to Aston Villa and the club confirmed on Tuesday that the two England internationals are yet to return to training.
Ole Gunnar Solskjaer's side will be hoping that both Shaw and Maguire can make it in time of the visit of Unai Emery's men at Old Trafford, with United already missing defender Aaron Wan-Bissaka due to suspension.