Casemiro accepts that Real Madrid have endured a disastrous start to the season, and admits that they are not playing well.
Los Blancos sit seventh in La Liga, having taken 14 points from a possible 27.
Nevertheless, reports have suggested that Julen Lopetegui could be sacked by the club if Real suffer an embarrassing result in the first Clasico of the season this weekend.
"You have to be honest, we're not playing well," Casemiro said.
"But you have to trust these players and the coach. We are not in a good run, but we have to work and overcome this situation."
However, Casemiro is looking forward with optimism as they prepare for the crucial clash with Barca.
He added: "The result has to give us confidence. We know we are not in a good moment, but we have added three points and we have to think about Barcelona."
The Brazil international has been ever present for Real so far this season, making a total of 11 appearances in all competitions.
Casemiro joined Real in 2013, and has won one La Liga title as well as four Champions League trophies, plus the Copa del Rey and two UEFA Super Cups.