This news is just a sweetener for the transfer market. Casemiro will not be interested in joining Manchester United if the conditions of the club you mention are still as they are today. Manchester United in my opinion is a club that has no goal to achieve as long as it is managed by the Glazer family. They only have a goal around the income that will be obtained. Casemiro is a great player. It would be a shame if he joined.
but there are also rumors of Casemiro's readiness to leave Madrid and play for United. but it looks like the price United will have to pay will be very high.
United seems to have failed a lot in the transfer market this season. De Jong and Rabiot are also reportedly not going to join United because there is no good agreement.
That would be actually amazing for everyone involved. Real would get some money and already have players ready to take his place, Casemiro would get a place where he could be seen as a savior that would help a team get a lot better, and United would get a player that can replace Pogba and then some because he is great.
This would be a win-win-win basically as long as United is willing to pay for him, and as we can see from what has happened this summer, Glazers do not want to spend a dime, and that is not how you get a better team, you need to spend a lot of money to become better, and I mean A LOT because they sucked so bad last year that they need to spend at least 100+ million more to be a decent team. From second ranked team to a 58 point team in a single season.