Without Casemiro, Manchester United will lose balance in midfield. Casemiro absence is a loss for Manchester United, considering that Manchester United's winning percentage is quite high when Casemiro appears.
This has made it difficult for Manchester United to find a suitable replacement for him, but I believe Sabitzer, McTominay, or Fred are capable of replacing Casemiro role in midfield even if they don't completely cover the midfield properly. Erik Ten Hag knows what he is doing and will handle it well.
Casemiro was not injured. He is still fine. He will not be absence from the match against sevilla. Mc tominay is not as bad as you think. Sabitzer injured and fred is a clown. he must not be included in the main squad by ten hag. Tominary is still become the main choice by ten hag after casemiro but since casemiro was not even injured and what's next? did you still try to imagine if he gets injured? Did you see the list of injured players from manchester united before?
I guess if you have not seen the list and you shall try to do that.