Speaking ahead of the sides' meeting in the DFB Cup semi-finals on Tuesday night, the veteran Bayern tactician, who spent two years in charge of Leverkusen between 2009 and 2011, was fulsome in his praise of Leverkusen's development under Heiko Herrlich this term.
"Bayer are a team with a real future," he said. "They're one of the candidates to be champions next season. When they become a bit more consistent, they're a side that can finish at the very top."
Watch: Enjoy Heynckes' top five moments as Bayern boss!
Heynckes attributed Bayer's upward curve - the club currently sit fourth having finished last season in 12th - to the work done by Herrlich.
"He's worked well wherever he's been, whether that's a big club or a small club. Herrlich is doing very well, in an unfussy fashion. He's doing a really good job. You can always see when a very good coach passes on his character, knowledge and personality to a team."
Heynckes knows plenty about coaching clubs big and small: as well as boasting Bayern Munich, Real Madrid and Leverkusen on his CV, he has also led the more modest Tenerife, and turned out for Hannover as a player.
Watch: Heynckes shares his thoughts on Niko Kovac appointment
Bayern's visit to Leverkusen – "It's not any old game for me; it's always nice to return to a place you were very happy," said Heynckes - is the latest in a succession of Bayern matches against Heynckes' former clubs.
Having beaten Borussia Mönchengladbach 5-1 on Matchday 30, the current champions take on Leverkusen in the DFB Cup last four, before meeting Hannover in the Bundesliga, Real Madrid in the UEFA Champions League semi-finals and then on Matchday 32 Eintracht Frankfurt, where Heynckes worked in the 1994/95 season and where his successor in the Bayern hotseat, Niko Kovac, is in charge.