Manchester United fear Benjamin Sesko could be out for up to a month after limping off through injury against Tottenham Hotspur.
Ruben Amorim's side finished that 2-2 epic before the international break with 10 men after Sesko was forced off with a knee issue with United having made all their substitutions.
Sesko, who pulled out of international duty with Slovenia to begin his injury rehab at Carrington, has avoided serious damage but is still set for an extended spell on the sidelines.
Daily Mail Sport understands that while United have not put a fixed timescale on the £73.7million summer signing's return, sources are anticipating it could be at least three to four weeks out.
With Sesko only arriving this summer his bounce back ability from injury is a relative unknown to United staff and the hope is that the 22-year-old responds positively to treatment and can return at the moment Bryan Mbeumo, Amad Diallo and Noussair Mazraoui lead for the Africa Cup of Nations so as not to leave Amorim too short changed in attack.
Speaking in the immediate aftermath of the Tottenham game, Amorim was fearful of the extent of the injury.
'I'm concerned with the injury because it's in the knee,' Amorim said.
'We need Ben to be a better team. We have to check everything, we have to check what has happened with Ben.'
Amorim will have to get creative now with limited options at centre forward.
Matheus Cunha is most likely to fill in as an unorthodox No 9 - he started there against Tottenham - while Joshua Zirkzee, who has grown frustrated at such a limited role so far this season, is now likely to be required to step up.
Mason Mount is another who is going to need to stay healthy to plug the gaps that Mbeumo, Amad and Sesko will inevitably leave.
Sesko has taken a lot of criticism since arriving in England, not least from former Manchester United title winner Gary Neville.
He has scored twice and registered an assist in 11 Premier League games so far this season and United gambled on him as their only true No 9 in the squad.
Rasmus Hojlund, who wanted to stay and fight for his place, was pushed out on loan to Napol, while 17-year-old Chido Obi has spent the entire season thus far with the Under-21s to further his development.