The 24-year-old, who has one year remaining on his deal at the Allianz Arena, has been heavily linked with a move away since refusing to extend his contract back in January.
Consequently, Kroos, who helped Germany to World Cup glory recently, would be available on a Bosman next summer, and Rummenigge says that talks between the European giants are underway.
"There are talks between Bayern and Real," he told reporters. "We don't want to lose the player on a free next season."
Kroos scored twice and set up a further three goals to help Germany end a 24-year barren spell at the World Cup finals this summer.