I understand that Manchester United is far from playing their best football. With the way other teams are performing it will be hard for them to make the champoins league spot. What Manchester United should do is to take their focus off the top 4 and make sure they can make the Europa league next season. But they should focus more on rebuilding the team next season.
Rather than forcing to qualify for Champions or Europa League, it's better for them to develop their club first.
They need to find two wingers, midfielders and few defenders. Although Onana sometimes make mistakes, but we have Bayindir who can replace Onana. While the other positions I mentioned before, Manchester United really lack of good players.
It will be too bad for a team like Manchester United to stay without European football next season, that's why I said they need to make sure they secure Europa spot. They can buy players in the positions you just mentioned in January. It will be hard for Manchester United to attract quality players in the summer if they are not offering European football next summer.