Kahn, 44, told Gala magazine that while homosexuality was no "big deal" in German culture, it's "naive" to think it wouldn't be damaging within the context of a professional sport.
He said a gay player would have to deal with vitriol from fans of the opposite team every Saturday, TheLocal.de reported Thursday.
"The atmosphere is heated. There are rivalries, which can lead people to do nasty things. On top of that, how will it go down with sponsors? What will it mean for your career? The situation is more difficult than it appears at first glance," Kahn said.