The #MeToo campaign took off past year following sexual assault allegations against Hollywood mogul Harvey Weinstein.
The Santa Monica PD said it has turned over all interviews and notes to a special Los Angeles D.A. task force.
The first was said to have happened in the 1990s, but it wasn't reported until late a year ago.
Santa Monica police confirmed to United States entertainment website Deadline that the complaint was made by a woman who in November 2017 said she meant to file a police report over an alleged sexual assault in the 1990s.
The accuser said she consented to have sex with Stallone but not De Luca, and that Stallone threatened to "beat her head in" if she told anyone.
Trump's claim North Korea no longer a nuclear threat raises eyebrows
The summit, the first between a North Korean leader and a USA president, ended with the leaders signing a peace deal. The meeting was also a "defining moment" for Trump, leader of "the world's police at the moment", said Cabalza.
"My client categorically disputes the claim", Singer said in a statement at the time. "At no time was Mr Stallone ever contacted by any authorities or anyone else regarding this matter".
Risling declined to provide more details about the alleged assault or to clarify whether California´s 10-year statute of limitations applies in the case.
"We are looking into it and will gather information and whatever we discover will be passed to the district attorney".
Earlier last year, the Daily Mail reported that in 1986 a 16-year-old autograph-seeker told Las Vegas police she was sexually assaulted by Stallone and his bodyguard.
Attempts to reach his lawyer, Martin Singer, were unsuccessful Wednesday night.