Arthur Hodge, 53, says he suffered a broken back in the collision.
Hodge and his attorneys, the Cochran Firm, say Knott's has provided no information regarding the accident.
The ride remains shut down while state inspectors investigate.
Knott's Berry Farm says "Pony Express" was launched in 2008 and has never had any problems.
Ride manufacturer, Zamperla, which is based in Italy, will investigate whether any programming problems led to the accident.
California Division of Occupational Safety and Health is reviewing the ride's maintenance records and will interview ride operators.
Riders straddle the saddle-like coaster seat like a horseback rider. And automated restraint system presses against the rider's lower back, providing little support for the shoulders and back.