Kahn says both Bayern and Borussia Dortmund were offered the veteran by agent Jorge Mendes.
He recalled: "We briefly discussed Ronaldo at Bayern and probably Dortmund too. We also see the big picture in the Bundesliga. An important factor in attracting attention to the league are, of course, superstars like Ronaldo.
"He's one of the greatest of the last decade. But we quickly dismissed that."
Kahn also ruled out moving for Dortmund midfielder Jude Bellingham.
He added, "Of course I think Bellingham is an excellent player. With Kimmich, Goretzka, Sabitzer and Gravenberch, however, we are very well occupied in the position, so we are not worried at all."