Newcastle boss Eddie Howe said his side are "dangerously close" to not being able to field a team for their Premier League game at Everton on 30 December.
Forwards Callum Wilson and Allan Saint-Maximin both suffered injuries during the 1-1 draw against Manchester United at St James' Park.
Howe fears Wilson could be facing "months" on the sidelines.
Newcastle are 19th in the table, two points behind 17th-placed Watford.
"Callum's injury looks severe, weeks maybe months," Howe told BBC Radio 5 Live. "I feared for him when he went down with nobody around him. A pull, not a knock."
It's understood both Wilson and Saint-Maximin have suffered calf injuries.
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