Christian Benteke and Ron Vlaar are both likely to miss Saturday's home game with Swansea.
Benteke [knee] has been absent for Stoke and Palace matches.
Vlaar [calf], meanwhile, has missed the Fulham, Man Utd, Stoke and Palace games aswell as the second half at Southampton.
Paul Lambert hopes to welcome back Benteke at Sunderland on New Year's Day although the return date for Vlaar is less clear.
Asked if Benteke would make the Swans encounter, Lambert said: "No. He's still got that little problem with his knee. Hopefully after Saturday he will be okay.
"He will likely miss Saturday. But hopefully for Sunderland. We will see how he is feeling."
Asked if Vlaar would return at the weekend, Lambert continued: "No. Ron is still struggling with his calf.
"That's been a blow.
"When you look at the likes of Vlaar, Benteke aswell as Ashley Westwood and Jores Okore, that's the core we're missing. These are big players."
On the flip side, Lambert will be pleased to welcome Westwood back, who missed the Palace game through suspension.
He added: "Westy will come into the fray.
"We will see how the others are feeling and pick a team we think can win a game.
"Westwood is a big miss when he doesn't play. He might not get the credit he deserves but people might realise he's a big miss when he doesn't play."
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