Tuchel was given his first coaching chance by Heidel at Mainz.
Speaking to Goal, Heidel revealed how pleased he was when Tuchel won the Champions League in May.
"I was very happy for him," he said. "But I always predicted that Tuchel would be one of the best coaches in the world.
"It was not a big surprise for me, but he has arrived where he belongs."
Heidel was also at Mainz during Jurgen Klopp's time at the club, however, the sporting director does not take credit for the two managers' successes.
"I am proud of Klopp and Tuchel, not me," Heidel added. "I'm just happy about the path they've taken and that it started in Mainz."
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