Jetro Willems and Paul Dummett will miss the rest of the season through injury, Newcastle boss Steve Bruce confirmed on Monday.
Willems ruptured his anterior cruciate ligament in Saturday's 1-0 victory against Chelsea, while Dummett suffered a hamstring injury in the FA Cup third-round replay win over Rochdale in midweek.
"It's what we feared; he's ruptured his anterior cruciute and will miss the rest of the season," said Bruce of Willems.
"We've had bad news on Dummett too, it's not looking so good on him as well. It looks as if he's probably ruled out for the season as well with a tendon injury in his leg.
"So it's been a bad weekend in that respect. We wish them well in a hopefully speedy recovery."
With Willems on a season-long loan from Eintracht Frankfurt, it means the 25-year-old has potentially played his last game for the Magpies, though Bruce says Newcastle have not yet ruled out offering the Dutchman a permanent deal.
"The big thing now is to let him have the operation and let him recover, and we will review the whole situation in a few weeks," he said.
"I think it's a bit all too raw for us at the moment to even speculate or comment on what's going to happen."
Bruce, who is hopeful of clinching a loan deal for Inter Milan winger Valentino Lazaro, admitted his January transfer plans may have to change because of the misfortune of the two left-sided defenders.
"It's one of those ones where you say, unfortunately, maybe yes, we have to," said Bruce.
"With the news of Dummett and [Willems] and then, of course, Matt Ritchie played there Saturday but he's just been back after four months.
"So, we'll have a look in that particular area. It's unfortunate because Jetro was just settling in well and adapting to life in the Premier League.
"He's been a very decent player for us so we will miss him and we hope him a speedy recovery."