Ronaldo is desperate to quit United after one year back at the club.
The 37-year-old has been linked with Chelsea and Bayern this summer.
But Kahn has claimed it will be against their philosophy to sign Ronaldo.
He said, “I love Cristiano Ronaldo, fantastic player but every club has a philosophy.
“And I’m not sure if it would be the right signal for Bayern and Bundesliga if we signed him now.
“Such a move does not necessarily fit with our ideas.”
Bayern on Saturday, confirmed striker Robert Lewandowski, will join Barcelona next season.