Rafa Benitez reveals why Aleksandar Mitrovic will miss Newcastle's visit to Arsenal
The striker wasn't involved in Wednesday night's 1-0 home defeat to Everton.
And Mitrovic will sit out the 16th-placed club's game against Arsenal tomorrow.
"Mitrovic has a little problem with his back," said United manager Rafa Benitez.
Paul Dummett is in the squad after recovering from a long-term hamstring injury.
The defender has been sidelined since the first weekend of the season.
Benitez said: "Dummett is in the squad – he's been training. Dummett's fit to start if necessary. We have to decide if he's ready to start or not."
Dummett's defensive colleague Jesus Gamez is not in the squad.
Newcastle are a point above the Premier League's relegation zone after Wednesday night's 1-0 defeat to Everton at St James's Park.
The loss followed a home defeat to Leicester City.
"The main thing's to analyse what's going on and try to find solutions," said Benitez.
"These last two games ... you saw what Leicester can do, the way they play away well. Against them, we conceded an own goal with five minutes left and that is disappointing.
"Then we made a mistake against a team we were controlling.
"Both games they wasted time and managed the game the way we need to learn to do. We have to be disappointed because we're so close and it's a pity."