Bale was whistled at by Los Blancos supporters when he came on as a substitute in a 2-0 LaLiga win over Getafe at Santiago Bernabeu on Sunday (AEST).
The forward has only played five games for the leader in the Spanish top flight this season and Madrid fans were not impressed when he declared himself unfit for a Clasico hammering against Barcelona last month, before inspiring Wales to a World Cup play-off win over Austria four days later.
Bale has won the Champions League four times and LaLiga twice since arriving in the Spanish capital nine years ago, but his relationship with Madrid fans has soured.
The 32-year-old, who is set to leave when his contract expires at the end of the season, did not do himself any favours when he held a flag with the words 'Wales. Golf. Madrid. In that order' after helping his country qualify for Euro 2020.
Yet Madrid midfielder Casemiro has called on supporters to lay off Bale ahead of the Champions League quarter-final second leg at home to Chelsea on Wednesday.
The Brazil international said: "When you whistle one player, you whistle all of us. Football is about opinions, everyone has theirs, but I don't agree when a player on my team is whistled. We're all on the same side, we have to support him."
He said: "I didn't like the whistles the other day for Bale. He's a historic player for this club. He's scored a lot of important goals for this club.
"When you whistle a player like that, you're whistling the history of this club. I didn't like it. I think the fans have to support us."
Madrid will start the clash against holders Chelsea with a 3-1 lead but Casemiro says they must not think it is job done.
He said: "We have to go in to it with the idea that it's going to be a very difficult game. We had our best 90 minutes of the season in the first leg, but we can't be complacent, especially given the coach's words about them.
"I'd like to ask the fans to get behind us because it'll be difficult as we're up against the champions and we respect them. We have to give our all along with the fans because it'll be very, very difficult."
Casemiro said: "When talking about Real Madrid, we always talk about winning everything. Everyone wanted to win a title at the start of the season, to be in the knockout stages like this and 12 points clear in LaLiga. We're working hard, but we've still got the hardest part to come."