Mel Gibson faces potential jail time if Los Angeles sheriffs find evidence supporting his former girlfriend Oksana Grigorieva's claims the Australian-raised Oscar winner assaulted her.

Grigorieva, a Russian singer who had a child with Gibson in 2009, contacted the LA Sheriff's Department last week and an investigation was launched on Monday.

Grigorieva alleges she was left concussed and had one tooth knocked out and another chipped when Gibson struck her during a violent dispute in January.

"I can confirm there is an investigation," LA Sheriff's Department spokesman Steve Whitmore told AAP.

"We opened it Monday.

"It was brought to our attention by the alleged victim, which we interviewed Monday."

Gibson, 54, and Grigorieva, 40, are embroiled in a bitter custody dispute for their eight-month-old daughter Lucia, with alleged audio tapes of their violent altercations leaked to online websites.

In one tape, Gibson allegedly sprays Grigorieva with foul language and a racial slur that was condemned by African American rights groups.

"You look like a f***ing pig in heat and if you get raped by a pack of n*****s it will be your fault," Gibson allegedly screams at Grigorieva, according to website RadarOnline.

Jewish groups, still hurt by Gibson's anti-Semitic rant during a 2006 drink driving arrest at Malibu, also denounced Gibson's latest alleged outburst.

Gibson's lawyers have rejected the assault allegations and claim the actor-director-producer was attempting to prevent Grigorieva from shaking Lucia during the January incident.

If the assault charges are proven, California's court system often hands out jail sentences for violent domestic abuse perpetrators.

Whitmore said the investigation could take about a month and the information would be handed over to the LA District Attorney's office to determine if charges should be laid.

"It should take a month, maybe more, maybe less, and when we are done with it we will hand the information to the District Attorney," Whitmore said.

The investigation is the latest severe dent to Gibson's career and public image.

His Australian wife of 30 years and mother of seven of his children, Robyn Moore, filed for divorce in April 2009 citing irreconcilable differences.

On October 30, Grigorieva gave birth to Lucia.

Despite the apparent turmoil between Gibson and Grigorieva in January, their break-up was only confirmed in April.