Zehnder was Raikkonen's boss when he first came into Formula 1 as a 21-year-old with Sauber, and 18 years on, the story remains the same with Zehnder still at the helm of the Swiss squad.
He has revealed Raikkonen, who returned to his former team from Ferrari at the start of the 2019 season, drives "without instructions".
"Kimi drives without instructions," Zehnder said on Raikkonen, who of course said on the Lotus team radio once: "Leave me alone, I know what I'm doing."
"Kimi does it all by himself. He understands everything. The engineers discuss with each other whether we need to change an engine setting, but at that very moment, Kimi changes it on his own. He knows exactly what he has to do and when."
Raikkonen has enjoyed a strong first season back at his former team and has completely outperformed his team-mate Antonio Giovinazzi - who has scored just one point - with Raikkonen scoring 30 points.