Chelsea signed Penders before agreeing to loan him back to Genk for the season.
Transfer expert Fabrizio Romano reports Bayern had scouted the 19-year-old for months, but Chelsea jumped in first.
The Belgian signed for the Blues for a fee of €20m and was then loaned back to Genk.
Last week, Genk teammate Tolu Arokodare told Tribalfootball.com of Penders: "He is a good person, a good professional and he is very hardworking. We should expect the best from him.
"I must admit that it is difficult to score against him in training and we do our best to help one another improve.
"We should expect nothing but the best from him and talking about our reaction when Chelsea signed him. Well, we were not really surprised because we know the qualities he possesses."