Lewandowski has emerged as a reported target for Madrid, with Karim Benzema enduring a difficult season in front of goal in La Liga.
The Poland international changed agents earlier in the year, linking up with the renowned Pini Zahavi in a move some suggested was made to facilitate a transfer to the Spanish giants.
But Rummenigge is calm about the situation, certain the striker will be pulling on a Bayern jersey again next season.
"They do not have to worry about Robert Lewandowski and the relationship with Bayern," Rummenigge told Kicker. "We have a very good one.
"We know what we have in Robert Lewandowski. I am very happy that we still have such a long-term contract. [There's] no need to worry - he will also play next season at Bayern Munich."
Lewandowski came in for criticism for his reaction to being substituted in Saturday's 3-1 win at Cologne, as he refused to shake manager Jupp Heynckes' hand.
But Rummenigge does not think Lewandowski should be penalised for expressing himself.
"You can't overdo it [in terms of reacting]," he said. "He is one of the best centre-forwards in the world, he proves that every year.
"If he has not scored for a couple of games, that's no problem either. I'm a big democrat, everyone can express his opinion."