The 'Face/Off' actor, 60, had his boy Weston Cage, 33, with 56-year-old actress Christina Fulton two years after they started dating in 1988, and sources say Nicolas' eldest struck her - after she was photographed out and about with a black eye and facial bruises.
Insiders have told TMZ Weston was "named a suspect in a battery report involving his mum" regarding an incident that occurred at her Los Angeles home on 28 April.
The alleged mother-son bust-up is alleged to have started as a verbal scuffle before quickly getting physical, a source told the outlet.
First responders were reportedly called to the actress' home but she is said not to have been taken to hospital.
According to TMZ, law enforcement is determining whether the case will be deemed as a felony battery.
But Page Six reported no arrests have been made, as Weston is said to have been gone by the time cops arrived.
Sources close to Christina told TMZ she was asked to help her son through an "emotional moment" and had him over to console him.
The outlet was also told she denied the allegations of a fight and requested privacy.
On Sunday, Christina was photographed at a parking meter with bruises all over her face - shown in images obtained by TMZ.
While the bruise under her eye was highly noticeable, there appeared to be yellow marks on her cheeks and forehead that were fading.
Christina and Weston were most recently working together to sue his estranged wife Hila Arounian for allegedly embezzling $100,000 and filing a "fraudulent restraining order" to stop her and Nicolas from seeing Weston's twin daughters.
A November 2023 lawsuit filed by Christina alleged Hila, who married Weston in 2018, was "emotionally abusive" and manipulative toward her now ex-husband to the point where he alienated himself from his family.
Weston alleged in his lawsuit Hila took advantage of him while he was in recovery from "mental health issues".
The former couple have daughters Cyress and Venice, and Weston is also dad to kids Lucian and Sorin from previous relationships.