Sunderland will be without Jewison Bennette for the rest of the season while Dan Ballard will miss two to three weeks, with the pair both picking up injuries on international duty.
Costa Rica international Bennette, 18, dislocated his shoulder in training and is now travelling back to the UK.
"It probably needs an operation and pinning," boss Tony Mowbray said.
Meanwhile, Ballard injured his hamstring in Northern Ireland's 1-0 Euro 2024 qualifier defeat by Finland.
Sunderland face Championship leaders Burnley on Friday when they return to action following the international break.
Mowbray's side are 11th in the table going into their final eight games of the season, seven points off the play-off positions.