The club could not be immediately reached for a comment.
Carlo Ancelotti was removed from his position as head coach of Bayern last week following a disappointing start to the season. A stinging 3-0 defeat by Paris Saint-Germain in the Champions League led the club to sack Ancelotti.
Heynckes had previously told German publication Kicker that his appointment was an act of friendship and not a comeback.
Two German coaches believed to be in the running to manage Bayern - former Dortmund manager Thomas Tuchel and Hoffenheim boss Julian Nagelsmann- have no prior experience with the club.
"Peter Hermann and Hermann Gerland will join Heynckes as his assistants".More news: NewsAlert: TransCanada cancels Energy East pipeline project
Asked whether his players turned on him at Bayern, Ancelotti concluded: "I respected all of them, but as a manager I have to make choices to put 11 on the pitch and seven on the bench".
Celtic travel to face Bayern on October 18, before the Bundesliga champions visit Glasgow a fortnight later.
Jupp Heynckes poseing with four trophies after giving his farewell press conference in Munich, southern Germany, on June 4, 2013.
Bayern will not want to just stand still and write off another season in which the club only wins the Bundesliga. "The coach was the biggest factor in our success", said former Bayern midfielder Bastian Schweinsteiger at the time.
Heynckes has not had a job in football since guiding Bayern to a historic treble in 2013, but confessed he simply could not turn the club down.