Sunderland goalkeeper Jordan Pickford has been ruled out for up to eight weeks with a cruciate ligament strain.
Pickford hurt his knee in a collision with Papy Djilobodji as Zlatan Ibrahimovic scored Manchester United's second goal in a 3-1 Premier League defeat on Boxing Day.
The 22-year-old completed the remaining eight minutes of the match but now faces a period on the sidelines.
"Jordan Pickford has good news and bad news," Moyes told a news conference.
"The good news is he hasn't ruptured his ACL, the bad news is he's strained it.
"We're looking at six to eight weeks, it's a major disappointment for him and for us because he's been saving us points.