The 23-year-old has not started a Premier League game so far this season, and has not featured at all since the derby defeat to Manchester City in mid-September.
The Slovenian has been struggling to shake off a shin injury – which is reportedly a different issue to the one which prematurely ended his 2025/26 season - and ruled him out for most of preseason.
Michael Carrick had hoped his injury issues were over, after staying behind for a focused rehabilitation programme during the last international break, but the situation now looks worse than first feared.
Further tests have hinted at wider damage to his leg, as per several UK reports, and he could now miss up to four months of action.
Carrick will offer an update on Sesko after tonight's UEFA Champions League trip to Como where the Red Devils chase a first win in seven games.