The anonymous sources identified the shooting victim as Walter Stewart and said he was rushed to Cedars-Sinai Medical Center shortly after the Friday shooting, TMZ.com reported Saturday.
Details regarding the shooting varied based on witness accounts as Somerville initially told police she believed her friend had been shot with a BB gun.
A valet who was near the scene of the shooting said the incident likely involved a small-caliber weapon.
TMZ.com reported the unidentified man who first called police from the party alleged the suspect threatened to shoot Somerville if she didn't hand over her purse.
The Web site said the companion of the actress, who played Mona on the NBC sitcom "Friends" was listed in stable condition.
Susan Sarandon 'very excited' about daughter's pregnancy
Dennis Rodman pledges to end trips to North Korea