The Germany international is one of the most in-demand players on the continent right now, having entered the final stages of his Veltins-Arena contract.
Unlike their counterparts, though, the Bundesliga champions have spoken publicly about their interest in Goretzka, which has left Heidel particularly unhappy.
"Bayern say Leon is a player of Schalke, but talk more about a player of Schalke than about their own [players]," he told German outlet Bild.
"As a result, [the transfer rumours are] fuelled again and again. We do not have to hear every day from the people of Munich how good the player is."
Goretzka has scored six goals in 12 senior appearances for Germany, playing a key part in his national side's victorious Confederations Cup campaign last summer.