Newcastle fear they have lost skipper Jamaal Lascelles for the rest of the season.
The defender suffered a suspected stress fracture againsg Spurs last week and the injury deteriorated this week, leaving him in a protective boot.
It is a major blow to relegation threatened United who face a gritty clash with Burnley on Sunday.
Bruce has welcomed star striker Callum Wilson back to full group training this week so he is available to start along with Allan Saint Maximin.
On Lascelles Bruce said: “We have lost the captain with a foot injury from last week against Spurs. That is a blow to us, leaves us a bit light at centre back.
“It is not looking so good at the moment he will have more scans, but he won’t play this weekend. It is a stress fracture, maybe, we think.
“It looked innocuous It got worse over the week. He’ll be in a boot for a couple of weeks. I hope it is not the end of the season for him, but it could be.”
Bruce added: “Callum and Allan are in the squad, and we have two days of training, but they have trained all week and that is good news they are available.”
Bruce faces a key dilemma over whether to start both Saint Maximin and Wilson. He explained: “That is the big decision, mindful they are muscle injuries, groin and a hamstring which you have to box careful with.
“Then again we also only have six weeks of the season left. I hope I make the right choice.
“It has been great to see them bounding around the training ground. Even top teams without their best players, it becomes a struggle.”
Bruce says the relegation fight is stressful. His side were in the bottom three when Fulham took the lead last Sunday.
Bruce joked: “My wife made Sunday lunch and Mitro scored. By the time I was eating my apple pie and custard, Fulham were 3-1 down.”
Talisman Saint Maximin has donated 60 care packages to NHS staff in Newcastle – calling them the “real heroes” of the past few COVID hit months.
The French winger lifted the spirits of Newcastle upon Tyne Hospitals NHS Foundation Trust staff a year on from the UK’s first lockdown.
He is in line for his first start since a groin injury saw him miss three games, and said: “We are in an incredibly fortunate situation as footballers as we know we are very privileged.
“The work the NHS staff and key workers at places like foodbanks have been doing here is inspirational and it makes you want to help as much as possible.”
He wrote in a message to staff: “To our real heroes, Game after game, I am fortunate to be warmly applauded by people from Newcastle! But this time I wanted to be the one who’s applauding, I wanted to applaud you, the best team of my city, the hospital medical staff of Newcastle! I have great respect for what you did! Thank you for being there for us.”