Anderson missed their Europa League win against Porto and may also be absent for the crunch Premier League game with Burnley on Sunday,
Forest are into the Europa League semifinals after a 1-0 win against the Portuguese giants and Pereira said: "Very sad situation. Everyone plays with Elliot in their heart.
“The players think about him. My condolences to the family. We are here to help him and we will see if he can play the next game.”
He added: “I said to my players in the dressing room, it is an honour for me to be the manager of this group because they have character and quality. Sometimes you have quality but you don’t have the team spirit.
“We are fighting for each other. When one of us is suffering, we are there to take care of them. That is why I feel proud of them.”
An early Morgan Gibbs-White goal earned the win on the night.
“Important to put smiles on the face of the supporters and connect the team with the supporters, unite the family and to believe,” Pereira said.
“We feel that we are creating something, the spirit to compete, to enjoy and to suffer together.”