Rafa Benitez is sweating on the fitness of Jamaal Lascelles and Ciaran Clark for Cardiff City's visit to St James's Park.
The Newcastle United defenders limped out of tonight's 4-2 FA Cup win over Blackburn Rovers at Ewood Park.
Sean Longstaff, Callum Roberts, Joselu and Ayoze Perez were on target as Benitez's side beat the Championship club at the second attempt.
Clark suffered a knee problem in the first half, and Lascelles pulled up clutching his hamstring after replacing him.
Benitez's staff will assess the pair ahead of Saturday's home Premier League game against Cardiff City.
"We need to wait tomorrow and see how they are, and if they cannot play then we will bring another one in," said Benitez.
"Jamaal Lascelles was limping, because he felt something."
Benitez doesn't believe Clark's injury is serious, though Lascelles' problem is potentially more of a concern.
“I think it is important to win, score four goals and go though," said Benitez, United's manager.
"At same time, you have some problems and you lose some players. We will see how they are in a couple of days. We won and everyone has to be happy, and we have to have confidence from this.
“Clark, I don’t think will very serious. Jamaal, we will have to wait. It's his hamstring, we will see. (Isaac) Hayden was fine."
Kenedy missed the game with a nail problem, but Benitez expects the winger to be fit for the Cardiff fixture.
Newcastle will face Watford at St James's Park in the fourth round of the FA Cup, and Benitez – who made eight changes at Ewood Park – will again rotate his squad.
"We have a squad that are trying to get through, and if we can do it the same way in the next round, we will be pleased with that," said Benitez.
Meanwhile, United Under-23 coach Ben Dawson belives that Roberts deserved his call-up to the the first-team squad.
Roberts – who made his debut in an FA Cup tie against Leicester City four years ago – scored on what was only his second senior appearance.
“For Callum, it’s been a while," said Dawson. "We look back to the Leicester game, when he was involved as a 17-year-old.
“He has had to bide his time, and he's been with us quite a while.
“It’s similar to Andy Carroll, where he came on at Palmero away and then had to wait two and a half years for his debut.
"Callum has had to work hard. He's had to be patient and persistent.
“He’s had some great nights and some good performances. The challenge for Callum is to do it consistently and against the more difficult opponents.
“We all know his ability on the ball, and he's improved his work-rate out of possession, understanding of defensive shape and how to help the team that way.
"We hope he's getting one step closer.”