Ruben Amorim fears Bruno Fernandes will be out for "a while" after the Manchester United captain was injured during Sunday's 2-1 defeat against Aston Villa.
Fernandes has started every Premier League game this season, but the Portugal midfielder is unlikely to extend that run any further following his injury setback at Villa Park.
The 31-year-old playmaker initially played on after pulling up with what appeared to be a hamstring issue just before the break, but he did not return for the second half.
Amorim ruled his influential star out of the Boxing Day clash against Newcastle, with severe doubts about his availability for the rest of the Christmas and New Year schedule.
"It's a soft tissue. I think he's going to lose some games. I don't know for sure, so let's see," Amorim said.
"You never control these things, so we'll see. He is a guy who is always fit so he can recover quite well, but I don't know."
While Casemiro will return from suspension against Newcastle, Bryan Mbeumo, Amad Diallo and Noussair Mazraoui are at the Africa Cup of Nations and Matthijs de Ligt and Harry Maguire are also sidelined for United.
Unai Emery heaped praised on Morgan Rogers after the star’s delightful double helped Aston Villa overcome Manchester United and extend their winning run to a 10th match.
The 23-year-old followed up last week’s impressive double at West Ham with another brilliant brace as Villa fought back from Matheus Cunha’s avoidable leveller to triumph 2-1.
Villa’s 10th straight win in all competitions was their seventh in a row in the Premier League, leaving them third in the standings and just three points behind leaders Arsenal heading into Christmas.
“The result was fantastic, and this is the most important thing,” boss Emery said.
“Emiliano Martinez saved with fantastic actions and Morgan Rogers played brilliantly, scoring goals, but overall we did a fantastic job tactically and in our game plan.”
Man United player ratings
Senne Lammens - 6/10: Beaten in the same place by two Rogers strikes. Little he could have done for either. Other than those, he was composed.
Leny Yoro - 3/10: Had to get out quicker for Rogers’ goal and show him down the line rather than let him cut inside and shoot. The second Rogers goal hardly covered him in glory either.
Ayden Heaven - 7/10: Played in the middle of a back three. Made up ground and did well to win the ball off Watkins after four minutes. Saved his team again three minutes later. Possibly his best performance yet but he’s playing in a defence conceding too many goals.
Luke Shaw - 6/10: A challenge against Watkins who tried to exploit the gaps between defenders, then against McGinn on the left. More touches than any player on the pitch as United dominated possession.
Patrick Dorgu - 7/10: Too slow on the ball early on, but grew into game. Crossed well for Dalot on 35 minutes and jumped forward to nick the ball which led to the equaliser. Hit a shot well himself on 59 and crossed perfectly for Cunha on 67.
Diogo Dalot - 6/10: Smart run on 9 minutes and a nice ball to Sesko on 11. Stayed high to help the midfielders and nicked balls. Shot on target in the push for an equaliser on 59. Defensively, not as impressive, especially on both Villa goals, but another reasonable game. Booked for a high boot on Ian Maatsen.
Bruno Fernandes - 7/10: Central to United’s first-half dominance, he had a shot deflected on 42. Pulled up with his hamstring before half time. Big blow as United's ever-present captain went off and his manager conceded could be out for some time.
Manuel Ugarte - 5/10: Played behind Fernandes and Mount. Lost the ball to Tielemans which led to an early Villa attack. Not the best start and hit a long pass to no one on 30. A little higher in the second half, when he was booked. Came off soon after.
Matheus Cunha - 8/10: Ran onto a second-minute ball and curled a shot just wide. Won the ball back to have a shot on goal on 33. Equalised before half-time with a sweet finish – and no way did United deserve to be behind. Had to score from a Dorgu cross on 67. Had another shot on target on 85.
Mason Mount - 7/10: A clever tackle after 10 minutes to win the ball back in a frenetic start where Villa had four shots in the first nine minutes. Jumped into the press and teased Sesko with an inviting cross. Smart ball to Dorgu on 67. United’s attack is better with him in it.
Benjamin Sesko - 5/10: Chance on 21 minutes after Fernandes put him through, though Villa goalkeeper Emi Martinez smothered him.
Substitutes
Lisandro Martinez (On for Fernandes, 45') - 7/10: Came off bench for fifth successive game. Looked comfortable, broke up Villa attacks, shot just wide on 55. Did well.
Jack Fletcher (On for Sesko, 72') - 7/10: Made his United debut. Bright. With half the team missing, younger plaplayers will get chances.
Joshua Zirkzee (On for Ugarte, 72') 6/10: Not surprised that he didn’t come on for Fernandes at half time. Hardly his fault, but he wasn’t bought for this United system. Did OK.
Shea Lacey (On for Yoro, 83') - N/A: Debut for the young and highly rated Liverpudlian. Had an 83rd-minute shot on target.
