Mane moved to Bayern from Liverpool last week.
Reschke recalled spotting Mane playing for RB Salzburg in a 2014 preseason friendly against Bayern.
"In 2014, Mané was an issue at Bayern Munich," he told Kicker. "We clearly saw him as an outsider. However, Franck Ribéry and Arjen Robben were absolutely set in these positions and better than Mané."
The then 22-year-old Mane was a "highly talented, explosive winger, a wild, untamed, incredibly fast, great perspective player", recalled Reschke, but not nearly as "totally mature".