Steve Bruce says both his front-line strikers Asamoah Gyan and Danny Welbeck are injured.
"It's unlikely they'll play again this season," Bruce said. "We're training with just 13 fit players now."
Both players were injured on Saturday against Wigan, while fellow striker Fraizer Campbell was recently ruled out for a year. The 18-year-old forward Ryan Noble is now the club's only recognised fit striker.
"Ryan hasn't played a lot of football," added Bruce, "and he's got a youth team game tomorrow."