TMZ claims the 26-year-old actor and his bodyguard ended up in a "very bad area" of the city during the early hours of Sunday morning after their car ran out of gas.
According to law enforcement officials, the pair were parked under the city's Harbor Freeway waiting for a tow truck. During this time they threw a bottle out of the window, which is said to have landed right next to a group of nearby "transients". The three men reportedly believed Zac and his security aimed the glass at them deliberately, causing them to confront the minder.
The actor reportedly claimed two of the guys attacked his security and when the star got out of the car to assist, he was hit in the mouth.
"It was the hardest I've ever been hit in my life," the former Disney star is believed to have told the cops.
It is not known whether there were any substances involved at the moment.
Despite the apparent violence, the website reports no one was arrested as law enforcements cited it as "mutual combat."
Zac's apparent injury comes after he broke his jaw after reportedly partying in his LA home last November.
He had secretly checked into rehab earlier in the year, although he has never confirmed what he was treated for.
To get himself back on track Zac is believed to have hired a sober coach, who allegedly attended the Academy Awards with him earlier this month.
"Zac had a sober coach with him the entire time ... to monitor what he was doing and to make sure he didn't partake in any substances like drugs or alcohol," a source previously told RadarOnline.com. "The coach was there to escort him to the bathroom or backstage, anywhere he needed to be where temptation might arise."