In an interview with German news magazine Der Spiegel, Rummenigge expressed his bemusement at changes pushed by Juventus chairman Andrea Agnelli, the president of the European Club Association (ECA), for a "pan-European league system".
"Why do we have to change anything at all about the competition?" asked Rummenigge in the interview, which will be published on Saturday.
"The Champions League is already the best competition in the world, and the most difficult to win."
Agnelli's concept envisioned a complete restructuring of all UEFA competitions from 2024, with internal relegation and promotion in a three-tiered system.
It also mooted the idea of playing matches at the weekend rather than in midweek, and proposed a new group stage format which would see four groups of eight teams rather than the current eight groups of four.
Rummenigge, himself a former ECA president, said that he was "no friend" of either weekend fixtures or an expanded group stage.
"The most important thing is that there are no weekend games, because this would create a big fight with the European leagues," he said.
He denied the magazine's claims that he had previously supported the idea of weekend fixtures in a leaked e-mail to Agnelli.
"I did not have a road to Damascus moment about this," he said.
He added that he expected "intense" discussions at next week's ECA shareholders' meeting, and urged European football's governing body UEFA to be "sensitive" in their decision-making.
UEFA are in consultations about the proposals, though president Aleksander Ceferin has ruled out the introduction of weekend fixtures.