Isco -- who was an unused substitute in a 3-1 Clasico win over Barcelona at Camp Nou -- was picked up by Movistar TV cameras talking to Luka Modric and Marcelo as they sat in the stands before the match.
"If [Zidane] has to take me off, he takes me off in the 50th or 60th minute, sometimes at half-time," Isco said, which led to laughter from his teammates. "If he has to bring me on, he brings me on in the 80th minute."
The Spain international has made just two starts in La Liga this season.
Zidane said he had "no doubts" about the 28-year-old after the Cadiz display, saying it was "a bad day, we want to change things, and Isco first of all."
"We've never had doubts about [Zidane]. We win and lose together. It's not like if we lose once, we aren't with him. That would be easy. We aren't like that. We saw the result on Saturday," Kroos said.
Madrid's Clasico win eased the pressure on the coach after the team had suffered two surprise defeats in a row to Cadiz and then Shakhtar Donetsk in the Champions League.
Zidane had insisted he felt the support of the club -- and president Florentino Perez -- and denied senior players such as Isco had problems motivating themselves against so-called inferior opposition.
"I've won a lot of things with these players... I'll be with them to the death," he said last week.
"In those two games we lacked a lot of things, but not the attitude of my players. They are motivated to do things well."