Roy, one of four people shot by two assailants, was hit in the upper body in the Saturday incident, according to sheriff's investigators.
Roy was struck while shielding some kids who were at the scene, a source told USA Today.
The ex-pro basketballer and the three other victims were attending a party when the gunfire erupted, Lt. Joseph Williams of the Los Angeles County Sheriff's Department said Wednesday. Roy was treated for the non-life-threatening wound and has since traveled back to Washington State.
A motive for the shooting remains unknown. No arrests have been made.
Roy played six years in the NBA, five of them with the Portland Trail Blazers, before his career was derailed by injuries.
The Trail Blazers released the following statement regarding the shooting:
"Like many others, we're just learning of the injury suffered by former Trail Blazers player Brandon Roy in a shooting over the weekend in California. According to those reports, Brandon was wounded as a bystander, but is expected to recover. Our thoughts and prayers are with Brandon and his family during this time."
In the Trail Blazer's statement, the team said Roy was once nicknamed "The Natural," and remains a fan favorite. He is currently the head basketball coach at Nathan Hale High School in Seattle, the team said.
The Associated Press contributed to this report.