In an interview with Billboard, Warner, 44, called the comedian an important mentor and friend to him.
"He's one of my mentors, and he's been very influential and played a big role in my life as a friend and mentor," he told the magazine. "Just as it's painful to hear any woman talk about sexual assault, whether true or not, it's just as painful to watch my friend and mentor go through this."
He added, "I can't really speak on any of the allegations because obviously, I was not there. The Bill Cosby I know has been great to me and great for a lot of people. What he's done for comedy and television has been legendary and history-making. What he's done for the black community and education has been invaluable. That's the Bill Cosby I know. I can't speak on the other stuff."
In September, Warner told CBS News that Cosby served as a mentor during those formative years on "The Cosby Show."
"I think one of the greatest advantages we had on the show growing up was being exposed to Mr. Cosby -- being exposed to his work ethic, being exposed to how he handles the job of celebrity and living in the public eye...I think that all had a real significant impact," he said.
Cosby, 77, has not been charged with a crime and through his attorney has denied allegations, some of them dating back decades, that he drugged and assaulted women.
Billboard says its full interview with Warner, a Grammy nominee for his work on Robert Glasper's "Black Radio 2," later Wednesday.