The 24-year-old, who operates for the Bavarian giants in Germany, was the subject of reported interest from Real Madrid, although Bayern insist that no formal bid has been received.
Hainer also urged incoming-in-waiting Madrid president Florentino Perez not to "waste time" pursuing the forward. Perez is widely expected to be re-elected as the Spanish club's president.
Olise enjoyed a prolific 2025/26 campaign, registering 53 goal involvements in 52 appearances across all competitions for Bayern.
The Munich-based side maintain they have no intention of selling the winger, who remains a key figure in their squad.
"Michael Olise is a Bayern Munich player and he is on a long-term contract. We are not a selling club," Hainer told German outlet BILD.
"If Florentino Perez wishes to make us an offer - which has not been the case so far - he can save himself the trouble, not even for 150m euros or more."
