DEL MAR, Calif. - Jockey Edwin Maldonado sustained a collapsed lung and broken ribs in a training accident at Del Mar on Sunday, according to his agent, Sarah Wolfe. At midday, Maldonado was undergoing an operation to aid his breathing, Wolfe said. Maldonado was unseated during a workout shortly after his mount broke from the gate. Observers said Maldonado struck the rail in the accident. He was taken from the track in an ambulance and immediately transferred to a hospital in nearby La Jolla. :: Enjoy news and analysis from DRF? Get handicapping analysis, real-time coverage, special reports, and charts. Unlock access with DRF Plus. The injury comes at a time when Maldonado, 33, has struggled to regain a position in the top 10 in Southern California. Through Saturday, Maldonado had won three races from 73 mounts at the current Del Mar summer meeting. Earlier this year at Santa Anita, Maldonado was fourth in the standings at the winter-spring and spring-summer meetings.  He has won three riding titles, most recently tying with Rafael Bejarano at the 2013 spring-summer meeting at Hollywood Park.