I have mixed feeling on this. On one hand I disagree in spending silly money on a 30 year old DM. On the other hand I never bought this McSauce tripe. I always thought that he was championship level, that the only reason he's playing is his passport and that we needed to add some serious quality in the DM role.
Now back to the question. Casemiro is a fantastic addition to the team. The guy is the Rolls Royce's of DMs, he's experienced and on top of that he knows Varane and Fred very well. I am expecting the latter two to improve significantly with him around especially Fred. The Brazilian can now switch into a box to box role and become the player we spent 50m upon. We all know that Fred has got great attitude, he can fill gaps and is built around the pressing game. What he lacks is that defensive discipline and positioning that Casemiro will provide in bucket loads.
So if I was ETH this would be my defensive core
DC: Martinez-Varane. Both are quick, they are quite intelligent and can play in a high line.
DM: Casemiro
B2B: Fred
AMC: Eriksen or Bruno
Bruno is my biggest question mark. On one hand he's a fantastic player, a proper assist and goals machine. On the other hand I think he's becoming too big for his own good. He's fixated with this shadow striker role which quite frankly is not what United need and certainly its not doing him any favours. Sure United do need goals. However the ball need to reach the striker first. So I'd say give Bruno a break and let Eriksen play a couple of games there.