Erik ten Hag revealed Casemiro is in a "race against the clock" to make the Manchester derby and says the squad is behind Alejandro Garnacho as he faces a potential ban for a social media post.
The eyes of the footballing world will be on Old Trafford this Sunday afternoon as treble winners Manchester City look to end the Red Devils' unconvincing three-game winning streak in all competitions.
United have stumbled to those victories against Brentford, Sheffield United and Copenhagen, with a vastly improved performance required if they are to lay a glove on Pep Guardiola's men.
The midfield battle looks key and Ten Hag says his side may be missing Casemiro for a third straight game, with an ankle injury sustained on Brazil duty putting his place in jeopardy.
"Aaron (Wan-Bissaka is back) in training today and Case is a race against the clock," Ten Hag said. "No, not 100%."
Casemiro had trained ahead of Tuesday's Champions League clash against Copenhagen - a group match he was unable to play in due to suspension.
The Red Devils were made to sweat in a narrow 1-0 victory against the Danish champions, with Andre Onana producing a stoppage-time penalty save that saw the under-fire goalkeeper mobbed by team-mates.
Garnacho later uploaded a photo on X, formerly known as Twitter, of the United players celebrating with the Cameroon international with a caption featuring two gorilla emojis.
But the Football Association has punished players in the past for making racial references on social networking sites and is understood to have sought Garnacho's observations.
"Not (concerned about a ban) in this moment," Ten Hag said. "We are talking with the FA.
"But what you see and I can confirm that and I want to emphasise, we are together, we are United and we have seen that in the post of Andre Onana."
Former United striker Edinson Cavani was banned for three games and fined £100,000 in 2020 for using the Spanish phrase 'Gracias negrito' - which translates as 'thanks little black' - below a friend's Instagram post.
The Uruguay striker also underwent a two-hour face-to-face training course for a comment said to be a term of endearment in his native Uruguay.
The previous year Bernardo Silva was given a one-match ban and fined £50,000 by the FA for his tweet to Manchester City colleague Benjamin Mendy.
The Portuguese tweeted an image of a young Mendy alongside an image of the cartoon brand mascot of Spanish confectionery brand Conguitos, with the caption "Guess who?"
Silva could be lining up at Old Trafford against Garnacho this weekend in the 191st Manchester derby - a match that could define United's mood at a key stage of the season.
Meanwhile Pep Guardiola has condemned the "vile chanting" by two City fans in the wake of Bobby Charlton's death.
"They don't represent us," Guardiola told reporters on Friday. "The alcohol makes bad, bad things in people."
City suspended two minors from attending games after video emerged on social media of them chanting "Bobby's in a box" during their team's win over Brighton & Hove Albion on the same day at the Etihad Stadium.
"What represents us is that the next time I go to Old Trafford to sign the book on condolences on behalf of Manchester City," Guardiola said. "We have a huge respect for Manchester United and especially the icon and the figure that is Sir Bobby Charlton.
"Our condolences are with his family and with Manchester United. They always are and always will be there."
