Casemiro is so important to Real Madrid that Zinedine Zidane's success is heavily dependent on his availability, according to Real Betis head coach Gus Poyet.
The two teams meet at Benito Villamarin in LaLiga on Saturday as under-pressure Zidane has to make do without the Brazil midfielder, as well as injured trio Sergio Ramos, Luka Modric and James Rodriguez.
But Poyet believes it is Casemiro's absence that has been the main reason for Madrid's recent poor form.
Indeed, the 24-year-old has been out for a month and Madrid have drawn all four of their matches since he last played.
Poyet told The Independent: "People say four months ago Zidane was a better coach - no.
"Zidane four months ago found the solution to Madrid's problems by playing Casemiro and he won the Champions League.
"Casemiro gets injured and now they say he is a disaster."
Betis are down in 15th position going into the weekend, but are yet to taste defeat after three matches at home.
Poyet is eager to avoid a similar result to the 6-2 thrashing his team suffered the last time they faced a title-chasing side, Barcelona, at Camp Nou on the opening weekend of the campaign.
Asked if he would tell his players to enjoy the occasion, he said: "Well, if things had gone well for us against Barcelona earlier in the season then I would say yes.
"But I wrote 'enjoy it' on the board before the game and we were hit for six! So 'enjoy' - no, that word is out!
"When I was a player here in Spain at Zaragoza the first thing you would look at when the fixtures came out was when you were playing Madrid and Barcelona.
"I wanted to play those games. So this week I imagine the players will have been thinking, 'Train well, pay attention to the ideas and then play'."