Martin's family said in a statement that doctors are hopeful the latest surgery will help with fluid build up in her abdomen. A previous surgery removed about two litres of fluid.
The gold medal hopeful crashed after a mechanical problem during a final practice with the U.S. team in California July 30. She suffered a severe liver laceration and a collapsed right lung, injuries that initially were deemed life-threatening.
USA Cycling announced last week that 19-year-old Brooke Crain would take Martin's place on the Olympic roster.
The BMX competition begins Wednesday with seeding runs.