1108 GMT January 22, 2020
Heynckes is currently enjoying his fourth stint as Bayern head coach, having taken over from the sacked Carlo Ancelotti in October, FourFourTwo magazine reported.
The 72-year-old has made a huge impact on Bayern's fortunes, with the club 17 points clear of second-placed Schalke at the top of the Bundesliga, with a DFB-Pokal semifinal and Champions League quarterfinal coming up.
Heynckes only has a contract until the end of the season, however, and Van Gaal – who won three trophies during a two-year stint as Bayern boss between 2009 and 2011 – claims the 72-year-old should call time on his career in May.
"If Jupp stops in the summer, it would be very reasonable, and I cannot imagine him going on and on when he turns 73," Van Gaal told the Bild am Sonntag.
"It's always better to quit at the peak of his career, if he does after this season then he is a god in Bavaria.
"Heynckes makes the difference with his personality, his philosophy and his behavior to the players."
Van Gaal was sacked by Bayern in April 2011 – his tenure at the club marred by a tumultuous relationship with president Uli Hoeness.
But despite reaffirming his dislike for Hoeness, Van Gaal acknowledged that Bayern has gone from strength to strength under the former Germany international's stewardship.
"Heynckes is the leader of this team, although Uli Hoeness always thinks he is the leader of FC Bayern, but that's not the case, because the leader is always the coach," Van Gaal said.
"Although I could not work with Uli, I have to say that he and [Karl-Heinz] Rummenigge are doing a fantastic job at Bayern and have a great chance of winning the Champions League."