Marcos Rojo suffered a dislocated shoulder as Manchester United manager Louis van Gaal's defensive options were further depleted as his side lost 1-0 to rivals Manchester City.
Rojo had to be taken off early in the second half - after Chris Smalling had earlier been sent off - to leave United seeing out the game with Michael Carrick and Paddy McNair in central defence.
Afterwards, Van Gaal confirmed Rojo's injury, saying: "The shoulder is out so you never know how long that is out. You never know how long that will take I have to wait until tomorrow, I think, but he shall not play against Crystal Palace I think."
With Smalling and Rojo set to be out for next week's clash against Palace at Old Trafford, Van Gaal may be forced to field a patched up backline from the start but he insists they will manage.
Meanwhile, Van Gaal defended Marouane Fellaini against suggestions that the Belgian midfielder may have spat at Sergio Aguero.
Social media was left abuzz, speculating over whether footage of a first half incident in which Fellaini stood over the fallen Aguero, accusing him angrily of having dived in the area, also featured him spitting at City's match-winner.
Fellaini was enraged by Aguero's tumble in the box under his challenge, turning to remonstrate angrily with him after the referee Michael Oliver had turned down the appeal.
"I've heard that it is a question on social media but already that if he (Fellaini) is shouting and sometimes when you shout, there's a little bit of - how do you call it, saliva? - with it. I don't think he's a spitting figure," said Van Gaal.