Rafa Benitez has lost two defenders to injuries at Ewood Park tonight.
Jamaal Lascelles came on for Ciaran Clark at the break after he suffered a first-half injury against Blackburn Rovers in the FA Cup third-round replay.
But Lascelles pulled up soon after coming on, and lasted just 10 minutes.
And Benitez, United's manager, had to replace Lascelles with Isaac Hayden in a second enforced change.
Lascelles left the field with the game level at 2-2.
Sean Longstaff and Callum Roberts gave Newcastle a two-goal lead, but Blackburn netted twice before the break.