If the investigation concludes the allegations are false, they will change the 'Expendables' star's status to a victim.
And Sylvester's lawyer has already confirmed they will be pushing for the woman to be prosecuted for filing a false report.
The 'Creed' actor can't take any criminal action until the investigation is complete, but he has been told he can pursue civil litigation immediately.
News of the investigation comes a month after the actor's spokesperson Michelle Bega claimed the events categorically "never happened".
She said: "This is a ridiculous, categorically false story. No one was ever aware of this story until it was published today, including Mr. Stallone. At no time was Mr. Stallone ever contacted by authorities or anyone else regarding this matter. It never happened."