Josh Hutcherson "got kicked in the side of the head" by his co-star Jennifer Hutcherson.
The pair are currently promoting their upcoming sci-fi action drama The Hunger Games.
Josh and Jennifer shot several vigorous scenes while filming, but the concussion the actor sustained didn't happen while the camera rolled.
"The only time I got hurt [on set] was when I got kicked in the side of the head by Jennifer," Josh told E! Online. "We were hanging out and she was like, 'I can kick over your head' and I was like, 'No way,' she said, 'Watch!' But then she kicked me right in the temple."
Josh's brain injury was mild and he has no ill feelings toward Jennifer.
"She felt so bad. She was crying," Josh explained. "I've had a couple of concussions before so I knew what it feels like when it happens. We had to have a neurologist come in. It ended up being a very mild concussion, but still it was a concussion. [I'm now feeling] 100 percent."
Josh is more concerned about the possibility of receiving excessive attention after his and Jennifer's new movie reaches cinemas.
"People keep telling me to get ready for it," Josh said. "I don't think there's anything you can do to get ready for it."
The Hunger Games will be released in the US March 23.