He had all the time in the world to comeback in the best shape as possible after shoulder surgery. If his back is still not what it was or his ankle/foot, then what steps have been taken by him, the player and person, first and foremost, which then the club can support him?
There's no real hate towards Marcus the person, it has recently been his commitment, dedication, professionalism, and effort for the team and his teammates. Players will make physical mistakes and have poor form, that's acceptable. What's not acceptable is the effort you're putting in, especially on matchdays when you're the number 10 of Manchester United. You are one of the highest earners at the club and in the PL. The club has put a lot of belief, time, effort, and support for a player like him to be a central figure in the football they play.
Being played "out of position" is being played for the greater good of the team. He's lost out to Elanga many times this season. That's an issue and shouldn't be happening. He's being given the time to get back into form, like the past 7 months. His performances that he showed even during his debut season(s) was good, but as EtH said yesterday and multiple times, "good is not good enough". He's had to raise his game another level or two, coupled with consistency. He's been unable to do that, and as a central figure in the team, the team has suffered especially this past season.
Marcus can only improve and get back to his best at least. But by god, while his form and confidence has been low, effort shouldn't be questioned. RVP didn't score for like 10 games for United. He had a rotten streak, but he still put in the effort and desire to play for the team. Do whatever it takes to win for the team. That's the difference.