Christian Eriksen will be out of action for up to three months due to the ankle injury he suffered in Saturday's FA Cup win over Reading, Manchester United have confirmed.
Eriksen was on the receiving end of a heavy tackle from Andy Carroll in the second half, with the Reading forward surprisingly avoiding a yellow card.
Carroll was later sent off for another two forceful challenges.
Eriksen walked away from the incident to play on briefly, but he was soon replaced and later spotted leaving Old Trafford on crutches, with a protective boot supporting his left ankle.
United boss Erik ten Hag offered little insight after the match, but following examinations the club believe it is serious enough to potentially rule him out until May.
A statement read: "Manchester United midfielder Christian Eriksen is expected to be out of action for an extended period because of an ankle injury sustained in our Emirates FA Cup victory over Reading on Saturday.
"While investigations are continuing, initial assessments indicate that Eriksen is likely to be out until late April or early May."
The absence of Eriksen will be a major blow to United and Ten Hag, as the Danish midfielder has been a key component of the side since his arrival on a free transfer in pre-season.
Bruno Fernandes (2,603) is the only outfield player to spend more minutes on the pitch than Eriksen (2,274) across all competitions for United this season.
It is a similar story in terms of chances created, with Eriksen's 53 bettered by only Fernandes' 81, highlighting the Dane's creative importance, particularly from set pieces.
Eriksen ranks highest in the squad for assists (nine), however, three more than Fernandes.
If the 31-year-old does not play again until the start of May, he will have missed at least 18 matches in all competitions.
That total will increase if United progress in the FA Cup, Europa League and EFL Cup – they are just 90 minutes away from the final of the latter after winning 3-0 away to Nottingham Forest in last week's semi-final first leg.
The return game at Old Trafford on Wednesday will be the first match Eriksen misses.
The absence of Eriksen further stretches United's midfield options after Donny van de Beek was ruled out for the season at the start of January.
It leaves Fernandes, Fred, Casemiro and Scott McTominay as their only recognized senior midfielders, potentially requiring 17-year-old Kobbie Mainoo – who has made two cup appearances but is yet to make his Premier League bow – to step up unless they delve into the transfer market before the window closes on Tuesday.