Ruben Amorim has confirmed that Mason Mount picked up an injury against Newcastle United on Friday night.
Manchester United celebrated Boxing Day with a hard-fought 1-0 win against the Magpies, overcoming their opponents thanks to Patrick Dorgu's first-half winner.
The Red Devils came into the match with a severely depleted squad due to injuries to the likes of Bruno Fernandes and Kobbie Mainoo, but matters were made worse when Mount was substituted at the interval.
Amorim confirmed that the Englishman was forced to withdraw at half time, when he told reporters: "He felt something at half time. He wanted to go the second half but we can’t lose more players."
Mount's injury record is poor, with the midfielder having started just 13 Premier League games in the last two seasons at Old Trafford, and fans will hope that any setback is purely precautionary.
Manchester United injury latest: Why Ruben Amorim needs reinforcements
United are currently fifth in the Premier League with 29 points, and while the likes of Liverpool could move ahead of them by the end of the weekend, the club are in a strong position to challenge for a place in the top four.
However, Champions League football looks unlikely at the end of the season given Amorim's options in the squad are limited, with Bryan Mbeumo and Amad Diallo both at the Africa Cup of Nations.
Casemiro and Manuel Ugarte are the team's only senior midfielders available for selection, while centre-backs Harry Maguire and Matthijs De Ligt are both on the treatment table.
United have recently been linked with the addition of James Garner from Everton, but it would be surprising if they managed to get by with just a single signing in January.
Liverpool, Manchester United and Chelsea: Who will finish fourth?
While it is important that teams like Crystal Palace and Sunderland are not discounted in the race for the top four, it is fair to say that United's biggest challengers for Champions League football look likely to be Liverpool and Chelsea.
Liverpool are currently unbeaten in six games but they are dealing with numerous injuries throughout their squad, and they may reach a crisis point sooner rather than later.
Chelsea have the deepest squad of the three teams, but Enzo Maresca's side have been plagued by inconsistencies.
The Blues are almost certain to spend heavily in the winter, and perhaps the only way for United or Liverpool to beat the Londoners to fourth is to also spend significantly in January.