State Attorney Willie Meggs has scheduled a news conference at 2 p.m. Thursday in his office to announce his findings.
Meggs says investigators have learned as much as they can about the December 2012 incident.
ESPN first reported that the investigation had been completed.
A lawyer for Winston has suggested that the star quarterback and the accuser had consensual sex. But the family of the victim has accused the 19-year-old of rape.
Meggs has said he wanted to make sure prosecutors completed a thorough investigation before making a final decision. He has also said several times that it's up to prosecutors to determine whether there is a "reasonable" chance of conviction.