Defender Victor Lindelof needs a scan and is expected to be out for "quite a while", according to Manchester United manager Jose Mourinho.
Lindelof sustained a muscle injury on international duty with Sweden but played through the pain in Saturday's goalless draw at home to Crystal Palace in the Premier League.
The centre-back has been a regular starter for United this term, named in Mourinho's starting line-up for 11 Premier League matches and three Champions League games.
But the Portuguese will need to find an alternative for the 24-year-old as he is set to miss Tuesday's Champions League game at home to Young Boys and could be unavailable for a number of weeks.
"He will be out for quite a while," Mourinho told a news conference on Monday.
"An injury - a proper injury - that will keep him out for a while.
"If we have him for the Christmas period, when we need as many as possible, it will be good."
Jose confirms @VLindelof will miss Tuesday's #UCL match through injury, adding "he'll be out for quite a while." #MUFC
— Manchester United (@ManUtd) November 26, 2018
United are also without Argentina international Marcos Rojo for the visit of Young Boys.
"We have [Eric] Bailly and [Phil] Jones," Mourinho said.
"Marcos Rojo has some little injury, and Victor an injury, a proper injury.
"So Jones, Smalling and Bailly are the three we have."
