The spotter, who is said to have only started the job a few days ago, is being treated at Cedars-Sinai Medical Centre and is said to have suffered broken legs, broken arms and a broken back.
Beverly Hills police Sergeant Jay Kim said: "The crash occurred about 5pm on Santa Monica Boulevard near Elm Drive when a paparazzo following the pop star collided with another paparazzo on a motorcycle about a mile from the Four Seasons Hotel.
"Britney Spears was not injured and had no direct involvement in the crash. No arrests were made and no citations were issued in connection with the wreck, which appeared to be just an accident.
"Alcohol did not appear to play a part in the crash. The injured motorcyclist was taken to Cedars-Sinai Medical Centre with abrasions to the arms and legs. His condition was not immediately known."
One witness said: "The spotter was hit by a silver Range Rover and was literally smashed under its wheels. His body went into seizure and then it just stopped moving."