"Extortion allegations were brought to our attention [and] we're looking into it," L.A. Sheriff's spokesman Steve Whitmore tells PEOPLE.
Gibson, 54, previously claimed the Russian musician, 40, demanded cash from him and, if he didn't pay, threatened to leak recordings of him spewing racist comments and threatening her to the media.
A source says Gibson was planning to present evidence to detectives proving Grigorieva broke the law. He also asserted that she made false claims to police about his alleged abuse.
According to Grigorieva's rep, police aren't launching a full investigation, however. "Looking into something is very different than launching a formal investigation," Grigorieva’s spokesperson Stephen Jaffe, told PEOPLE.
Reporting by OLIVER JONES and KEN LEE