Aaron Wan-Bissaka has been ruled out for several weeks with a hamstring injury, Manchester United has confirmed.
The 25-year-old sustained the injury in United's 3-1 loss to Brighton on Saturday.
He only came on as a substitute in the 85th minute, having recovered from an illness he battled earlier in the week.
A statement from United said: "Further assessment will be needed to determine how long Wan-Bissaka will be out for, but initial indications suggest it will be several weeks."
This worsens United's injury woes as manager Erik ten Hag is without three of his full-backs, with Wan-Bissaka's injury coming after Luke Shaw was ruled out for a long period with a hamstring problem, while Tyrell Malacia has been injured since the end of last season.
United's only available natural full-backs are Diogo Dalot and on-loan Tottenham player Sergio Reguilon.
The club is also afflicted with injury crises in other areas of their squad as Sofyan Amrabat, Mason Mount and Raphael Varane are on the sidelines, marking a dreadful start to the season.