If she does pursue a fresh legal challenge, it could renew a bitter custody battle that dragged on for over a year and captured public attention with its allegations of physical and psychological abuse.
Grigorieva and Gibson have a daughter, Lucia, together. Under a settlement deal reached last August, the pair agreed to split custody of Lucia.
But the issue may not remain resolved. In the an explosive nine-page letter to Gibson obtained by TheWrap, Eszterhas claims that Gibson told him that he was friends with two FBI agents who were going to help him to kill Grigorieva.
(Editor's note: Highly offensive language follows.)
“You kept raging about your ex-girlfriend, Oksana Grigorieva, Luci’s mother, whom you always referred to as ‘that cunt’ and ‘that fucking bitch,'" Eszterhas writes. "You acted out for me the scene where you hit her. But you said you’d ‘just slapped her a little bit.'"
Eszterhas had been working with Gibson on a movie about Jewish hero Judah Maccabee, whose victory over Greek and Syrian armies is celebrated at Hanukkah. That film has been shelved by Warner Bros. over what the studio has attributed to script concerns.
In his letter, Eszterhas also alleges that Gibson repeatedly referred to Jews as "Hebes," "oven-dodgers" and "Jewboys" and described the Holocaust as "mostly a lot of horseshit."
Steve Jaffe, a representative for Grigorieva, declined to comment on any possible legal actions his client might pursue. He did indicate that he believed Eszterhas' allegations were valid.
"Eszterhas has a well-documented history of confronting people very specifically in highly detailed letters that deal with his business," Jaffe said. "It would follow that this seems authentic."
Asked about whether Grigorieva was taking new safety precautions in light of Gibson's alleged threats, Jaffe said, "I can't comment on that for obvious reasons."
A spokesman for Gibson did not immediately respond to a request for comment.
In the thick of their custody dispute, recorded conversations between Gibson and Grigorieva leaked online in which the actor threatened his former girlfriend with physical harm and peppered his conversation with racist remarks. They captured an emotional Gibson, frequently out of breath and threatening to put Grigorieva "in a fucking rose garden.”
After the tapes leaked, police launched an extortion investigation to see if Grigorieva was attempting to use the recording to bribe the actor. The inquiry resulted in no charges being filed against Grigorieva.
Gibson pleaded no contest in March 2011 to a misdemeanor battery charge stemming from their dispute. Grigorieva dropped her domestic violence claims against Gibson in May of that year.
He reached a financial and legal settlement in August with Grigorieva, under which the actor agreed to pay $750,000 over five years and split legal custody of Lucia. Gibson agreed to buy a house for Grigorieva and their daughter.
That was substantially less than the reported $15 million settlement offer Grigorieva previously turned down.
As part of the resolution, Gibson was sentenced to three years' probation and ordered to perform 16 hours of community service.
The actor hit back at Eszterhas' letter Wednesday, writing that the screenwriter's observations about his anti-Semitic behavior were "utter fabrications." He did not directly address the charges about Grigorieva.
"The Gibson letter seems to do everything but confront Eszterhas' allegations about anti-Semitism or his threats about Oksana," Jaffe said.