The entertainment news blog Radar Online said it obtained a tape from an anonymous source who provided an affidavit confirming the voice was that of the 80-year-old Sterling.
"You think I'm a racist?" Radar Online quoted Sterling as saying on what it reported was a secretly recorded phone conversation. "You think I have anything in the world but love for everybody? You don't think that! You know I'm not a racist!"
Radar Online included the recording in its report. Reuters could not independently confirm it was Sterling's voice on the recording.
Last month the NBA fined Sterling $2.5 million and banned him from pro basketball after the website TMZ.com posted an audio recording with a voice said to be his that made derogatory remarks about black people.
The comments sparked outrage from players fans as well as U.S. President Barack Obama, especially since Sterling was a team owner in a league that was in the forefront of racial integration in U.S. sports.
Sterling has yet to comment publicly. He could not be reached immediately on Thursday.
The NBA has initiated the process to terminate Sterling's ownership.
"How can you be in this business and be a racist?" Sterling said on the tape, according to Radar Online. "Do you think I tell the coach to get white players? Or to get the best player he can get?"
The Los Angeles Times reported on Wednesday that Shelly Sterling, Donald's wife and co-owner of the Clippers, said she intended to remain an owner of the team and has hired a law firm to represent her as the NBA moves to terminate her husband's ownership.
In 1981 Sterling purchased the Clippers, which were based in San Diego, for $12.5 million. The team is now estimated to be worth at least $575 million, according to Forbes, which compiles a list of professional sports team values each year.
The Clippers are currently tied with the Oklahoma City Thunder in the second round of the NBA playoffs at one game a piece. Their next match is scheduled for Friday.