Los Angeles County sheriff's spokesman Steve Whitmore said Thursday the unidentified cyclist ran into Hathaway's car a day earlier as it made a right turn.
"The Princess Diaries" star was a passenger in her black Audi being driven by her boyfriend Adam Shulman.
Whitmore says investigators determined the rider was a paparazzo because he was carrying a camera with a long lens.
Witnesses told deputies he was traveling fast but there was enough time for him to avoid the crash.
Whitmore says the paparazzo was at fault but no arrests were made.