Manager Michael Carrick said the club is still assessing the extent of the problem, and could not offer a timescale for his return. He told reporters:
“No, I think that just because you get setbacks in certain positions, you can't sign a player for cover in every one. We're not sure with Ben yet, he felt some pain after the Brighton game and we are assessing him at the moment.
“He definitely wasn't ready for today. I haven't got any more news to give you, just that he felt pain on his shin.”
The 23-year-old was withdrawn from United's Carabao Cup defeat to Brighton in midweek after feeling discomfort, and he was left out of the squad entirely for Sunday's draw with Fulham. Reports from Slovenia say he is due to have an MRI scan in London, with his country's outlet Ekipa warning that the type of shin problem involved can be unpredictable and difficult to resolve completely.
This is not a new issue. Sesko missed United's final three games of last season and the whole of pre-season with the same shin injury, a lay-off of more than two months, after signing from RB Leipzig last summer for a club-record fee.
He has made six appearances in all competitions this season, scoring against Everton and Sabah in the Champions League, and there is now concern in Slovenia that he could also miss the coming international break.
Manchester United have managed only one win in their first five league games, and Carrick's options up front are already stretched, with Matheus Cunha having deputised in attack in Sesko's recent absences.
The manager's comment about not being able to sign cover for every position suggests he does not expect reinforcements in January purely because of the setback, leaving United reliant on Sesko's recovery and the depth already in the squad.