BMX rider Arielle Martin of the United States has had surgery after injuring her liver and lung in a crash during practice last week that knocked her out of the London Olympics.

Martin's family said in a statement late Sunday that the medal contender "had a few setbacks" after she was upgraded from intensive care to a trauma unit. Martin had a severe laceration to her liver and a collapsed right lung in the crash during a final practice July 30.

USA Cycling did not announce the injury until Wednesday, when it said that 19-year-old Brooke Crain would replace Martin on the Olympic roster. The team left for London the same day.

The BMX competition begins Wednesday with seeding runs at the Olympic Park.

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