Casemiro's possible leave from Manchester United has been rumoured a lot recently. Now his name is called with Bayern Munich. However I don't think Manchester United should let him go that easy. Because Casemiro has strengthened the line between the defense and midfield incredibly much for Manchester United. In his absence the weaknesses start to be quite visible in this area.
It is just a rumor, there is no official statement from Casemiro or Man United management.
I am not surprised if there are some clubs interested to sign him. Casemiro played very well so far, he has a big role in the improvement of Man United midfield during this season. He is surely irreplaceable, not another midfielder who has the same capability as him. That's why I think Man United will never agree to let him go. He must stay at Man United, Man United needs him for the next season.