Bilbao have referred Bayern to Martinez's 40 million buyout clause in his contract.
Rummenigge said: "I'm not optimistic, to be honest. [Bilbao] president [Josu Urrutia] has always emphasised that he doesn't want to sell the player for a price under the clause.
"The asking price is immense. It's a fee that has never been paid by a German club."
He added: "There is no club in Europe that is willing to pay that price," he explained.
"You have to see the whole transfer business very rationally. There are some players who are worth it, but not many in this world."