Manchester United manager Erik ten Hag has said it could be "weeks" before Lisandro Martínez and Casemiro are available again.
Martinez has not played since September because of the reoccurrence of a foot injury initially suffered in April while Casemiro has missed the last two months with a hamstring problem.
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Both have since returned to training and were pictured on the grass at Carrington last week, but Ten Hag said they are not yet ready to make return to action.
"They are a long time already back on the grass and now they return back into team training but not fully, so partial," Ten Hag told a news conference.
"Now they have to make the next steps and that may take some days, I think even weeks."
With Mason Mount, Harry Maguire and Victor Lindelöf also on the sidelines, Ten Hag is preparing for Monday's FA Cup third round tie against Wigan Athletic with a similar squad to the one which was beaten 2-1 at Nottingham Forest on Dec. 30.
United have, however, been boosted by the return of Rasmus Højlund, who missed the defeat at the City Ground because of illness.
"He will return," Ten Hag said. "He dropped out shortly before the game [against Forest] and so he was a little bit unwell before the game. The day before we expected him to play and then he dropped out shortly before the game but he is back in training."
André Onana is set to start in goal against Wigan after United reached an agreement with the Cameroon FA to delay his release ahead of the Africa Cup of Nations.
United's decision to keep hold of Onana has raised questions about whether Ten Hag has confidence in his No.2, Altay Bayindir, but the Dutchman insists the summer signing from Fenerbahce will get his chance once Onana departs -- probably after the Premier League clash with Tottenham on Jan. 14.
"At some point André will go," Ten Hag said. "We are totally happy and we constructed this group of keepers because we are comfortable with this. We have confidence in them both and both are very good goalkeepers, both experienced at the highest levels.
"I think we can have a lot of belief that we have coverage, but not only coverage but competition between them. We are sure that if Andre has to go that we are good, we are in a good place and have a good replacement to fill that gap."