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.
Police in Santa Monica and Stallone’s attorney, Martin Singer, could also not be reached for comment.
The allegation against the star comes in the wake of the #MeToo movement that has focused attention on sexual harassment in Hollywood and beyond.
Singer in December told US media when the allegation first surfaced that his client “categorically disputes the claim and it is apparent that the woman filed the report to get a media outlet to publish the story.”
He acknowledged that Stallone had a relationship with the alleged victim while shooting a movie in Israel in 1987 while he was single.
The attorney said at the time that he planned to submit a claim against the woman for filing a false police report.
The #MeToo campaign took off last year following sexual assault allegations against Hollywood mogul Harvey Weinstein. It has since become a worldwide phenomenon.
Hundreds of celebrities and powerful people, including actor Kevin Spacey and longtime broadcast journalist Charlie Rose, have been accused of sexual harassment in the wake of the Weinstein scandal.