LOS ALAMITOS, Calif.-Quarter Horse jockey Sam Thompson was in critical condition at Los Alamitos Medical Center on Sunday evening after being thrown from his mount in a one-horse spill on Saturday, according to Los Alamitos track officials.\nAccording to a friend of Thompson's, the 35-year-old jockey suffered a neck injury. Members of his family were flying to Southern California on Sunday to be at his side. The extent of Thompson's injury was not immediately known.\nThe accident occurred in Saturday's eighth race. Thompson was riding Harems Dynasty who suffered an injury after a 300-yard race for maidens. Thompson was unseated, and may have been struck by Harems Dynasty while he was on the ground.\nHarems Dynasty was believed to be injured during the running of the race, according to Cody Joiner, an assistant to his father, trainer Mike Joiner.\n&#147;Sam realized that something was wrong but he probably did not know exactly what,&#148; Cody Joiner said in a statement released by the track. &#147;He tried to pull the horse up.\n&#147;Sam is one of my best friends in the world. We play golf every Monday. We never miss a Monday golf outing. Sam was excited to ride this filly. That's all he talked about (Saturday) morning. He didn't want any other rider to get on her in the mornings. We are all hoping for the best for Sam.&#148;\nThompson, 35, was sidelined earlier this year with a broken foot. He has won several major races at the Quarter Horse track in the last decade. Thompson was regular rider of the millionaire Corona Kool in the late 1990s and earlier this decade, and has won the Los Alamitos Million Futurity twice.\nFor many years, Thompson has been closely allied with former champion trainer Donna McArthur. This year, Thompson has won 28 races from 210 mounts that have earned $499,484.