Gibson, 54, and Grigorieva, 40, are involved in a bitter custody dispute over their 8-month-old daughter.
He is the subject of a Los Angeles domestic violence investigation.
Report: Mel Gibson's Ex-Girlfriend Demanded $10M
Mel Gibson Demanding Sex Act in Latest Tape?
Mel Gibson Slur vs. Latinos Caught on Tape?
On Tape: Mel Gibson in Death Threat vs. Ex?
Mel Gibson's Thickening Legal Quandary
Can Mel Gibson's Career Survive Latest Ugliness?
Did Mel Gibson Beat Up His Ex?
Now, RadarOnline has posted a potentially damaging photo of Grigorieva it says was taken a day after one exchange, allegedly of Gibson screaming and cursing at Grigorieva.
The woman is heard saying, "Hitting a woman when she's holding a child in her hands. Breaking her teeth, twice in the face! What kind of man is that?" "You deserved it," the man replies. "You're gonna answer. One day, boy, you're gonna answer."
The photo, says CBS News legal analyst Trent Copeland, shows a potentially abused Grigorieva in which, "There is some bruising that appears to exist on her cheek; there seems to be some damage to her teeth," and what looks like a fat lip, bruising, chips on the teeth.
"But we don't know when this photo was taken; we don't know whether Mel Gibson caused these injuries."
Also casting doubts, celebrity website TMZ, quotes sources who know the dentist who treated Grigorieva as saying he thinks the photo "has definitely been altered" and he "does not believe she was struck in the mouth, as she claims," though he does think she might have been "struck in the left temple, which caused her to bite down so hard, one veneer was completely knocked out and another was damaged. The (dental) charts reflect that Oksana's teeth were fully intact."
But, says "Early Show" national correspondent Hattie Kauffman, "If the picture can be authenticated, along with the rage-filled audiotapes (which also had the man on them making threats against the woman), legal analysts such as CBS News' Lisa Bloom say jail could be in Gibson's future.
"On the verbal threats alone," Bloom says, he "is looking at up to three years behind bars."