Following a disappointing sequence of results in the Spanish capital, which culminated in a 3-0 defeat to Tottenham in the Champions League on Wednesday, the Frenchman finds his job under threat after 18 months of success.
Heynckes, who spent time in that particular role during the 1997-98 season, believes that Zidane must be cut some slack against the backdrop of two successive Champions League final wins.
"Five weeks ago, Madrid were the best team in the world but now they’re criticised by everyone,” the 72-year-old said.
“That’s the rate at how things go at the moment, very quickly. The world of football should relax a little and be a bit more objective and realistic. I think that I’ve done it.”
Zidane stepped into coaching in January 2016, when he took over from Rafa Benitez as Madrid head coach, with the Bernabeu side third in the league, having lost three matches and drawn another four.
He enjoyed an instant turnaround, with a 5-0 win over Deportivo La Coruna in his first match in charge setting the tone for what would be a largely successful second half to the season. There was too much ground to make up on Barcelona, who claimed the domestic title, yet Real defeated local rivals Atletico on penalties in the Champions League final to write Zidane’s name into club folklore as a coach.
Twelve months later, not only did Zidane claim the Spanish title for the club, he also created history by becoming the first head coach to lift the Champions League trophy in successive years, with Juventus this time the victims as Madrid ran out 4-1 winners in Cardiff.
Madrid also won the World Club Cup by beating Kashima Antlers after extra time, and the UEFA Super Cup. They were only stopped in the Copa del Rey.
This season, they remain in contention on all fronts, although their sluggish start to the league campaign means that they find themselves eight points behind Barcelona ahead of matchday 11, in which they tackle Las Palmas on Sunday.