The Belgian midfielder has been in remarkable form for the Citizens this season, having scored six goals and provided nine assists in the top flight.
Asked by Kicker if Bayern were in need of a "super transfer" of over €50m, Heynckes replied: "What does super transfer mean?
"Paul Pogba cost Manchester United €105million. Does he play like this? Many alleged top players can and have still to learn. Bayern have to go their way with [Niklas] Sule, [Joshua] Kimmich, [Corentin] Tolisso or [Kingsley] Coman.
"For sure there has to come a player again for €40million or €50million, but today for €50million you don't get a finished player.
"For example Kevin De Bruyne. He did not play this well last season, but for him I would give shirt off my back. On this position you need such a player. De Bruyne is clearly the outstanding player in Europe at the moment."