Defenders Chris Smalling and Phil Jones sustained “long-term injuries” while on duty with England, says their Manchester United boss Jose Mourinho.
Jones, 25, injured a toe in an innocuous training-ground tackle, with reports claiming it involved Smalling.
Fellow centre-back Smalling, 27, was pictured with a leg brace following an injury also suffered in training.
United captain Wayne Rooney returns for Saturday’s game against West Brom after recovering from a knee injury.
The 31-year-old has missed the Red Devils’ past four games.
United will be without striker Zlatan Ibrahimovic and midfielder Ander Herrera, who are both suspended, and midfielder Paul Pogba, who has a hamstring problem.
Asked how long he expects to be without Jones and Smalling, the United boss said: “I don’t know. I think clearly they are long-term injuries and Pogba I have no idea.
“I know that Zlatan and Herrera have the last match ban, so it’s easy to say they will be available after the match.”
‘I am sorry for what I did to him’
Mourinho said he regretted the way he treated Bastian Schweinsteiger, and added he apologised to the midfielder before his move to the Chicago Fire.
The German World Cup winner, who joined United in 2015, trained with the reserves following Mourinho’s arrival in the summer, but was brought back into the first team in late October.
However, last week the 32-year-old was permitted a move to join the MLS side.
“He’s in the category of players that I feel sorry for something that I did to him,” Mourinho said.
“The last thing I told him before he left: ‘I was not right with you once, I have to be right with you now.’
“So when he was asking me to let him leave, I had to say ‘yes, you can leave’ because I did it once, I cannot do it twice.
“I will miss a good guy, a good professional, a good influence in training – a very good influence.”