State Attorney Willie Meggs has scheduled a news conference at 2 p.m. Thursday in his office to announce his findings. Meggs said investigators have learned as much as they can about the December 2012 incident.
"We think we have exhausted all investigative tools," he said.
Winston has led the Seminoles to the No. 1 ranking, and they will play for a conference title Saturday, with a shot at the national crown.
The quarterback also is the leading candidate for the Heisman, and many voters are waiting to see whether Winston will be charged with a crime before casting their ballots. The deadline for Heisman ballots to be turned in is Dec. 9.
ESPN has previously reported that DNA belonging to Winston was found in the underwear of the accuser. 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.
The fact that Meggs has scheduled a news conference - as opposed to getting a warrant for Winston's arrest - could be seen as a sign that he will not file charges.
Meggs said earlier Wednesday that the end of the investigation should answer some lingering questions about how the investigation was handled and why it took 11 months before prosecutors were notified.
"When you all look at this, when the dust all settles, you'll say 'Man, there were some things that could have been done back in December of '12 that could have cleared this up a whole lot easier than November of 2013," he said.
Timothy Jansen, the attorney representing Winston, said he does not know what Meggs will announce.
But Jansen said he hopes that following Meggs' Thursday announcement, Winston will finally address the investigation.
"If he looked at evidence we did, we feel confident he will find that Mr. Winston did nothing wrong," Jansen said.
Patricia Carroll, the attorney representing the accuser, did not immediately respond to a request for comment.
The alleged sexual assault was first reported to police in December. The family has said the victim did not know the identity of her attacker until early January, when she identified him as Winston.
The family has been sharply critical of the way Tallahassee police have handled the case. The family says they pushed to have a DNA sample taken from Winston only to be told by a police detective that it would alert Winston and make the case public. The family said Carroll was warned that by police that Tallahassee is a "big football town, and the victim needs to think long and hard before proceeding against him because she will be raked over the coals and her life will be made miserable."
Tallahassee police have defended their handling of the case and said it was placed on inactive status in February after police were told the alleged victim did not wish to prosecute the case. Carroll has denied that the woman wanted to drop the investigation.
The alleged victim was an FSU student during the December incident, but she left school after Carroll was told by police that information about the case was about to be released to the media.
Associate athletics director for communications Rob Wilson said the university did not have any comment Wednesday. The university is expected to address the matter sometime after Meggs' news conference.
Florida State policy dictates that a student-athlete is suspended from game action if charged with a felony until the charge is resolved "absent extraordinary circumstances as determined by the administration."
Winston was named Atlantic Coast Conference player of the year, offensive player of the year and rookie of the year this week after setting ACC freshman records with 3,490 passing and 35 touchdowns.
Associated Press writer Kareem Copeland contributed to this story.