Nevertheless, the former Real Madrid star's hefty weekly salary of £375,000 poses a significant obstacle.
No club that wants to sign him can afford even a third of his salary, which means he is a United player for the moment.
Casemiro was hooked at half-time in a 3-0 defeat to Liverpool at Old Trafford on Sunday.
United have signed Manuel Ugarte to take his place in the starting lineup in the near future.