He suffered multiple broken bones and a collapsed lung as a result of the accident, which occurred at Malibu Beach, TMZ reported.
Schwarzenegger was in intensive care, where he had been for several days. His condition was not known.
His parents began court proceedings this week to end their 25-year marriage, which broke down after it was revealed that Arnold Schwarzenegger fathered a child with another woman.
Earlier this week, the former California governor indicated in his divorce filing that he does not want to pay spousal support to Shriver or cover her attorney's fees.