A statement about event rider Darren Chiacchia's condition has been posted on his web site: "After breathing independently for a few hours, Darren had a temporary set back. He developed a fever and pneumonia causing him to be re-intubated and is now breathing with a ventilator. He continues to receive superior medical care and remains in critical but stable condition.
"The Chiacchia family wishes to extend their appreciation for all the concern and support."
The former Olympian suffered major chest injuries during a fall on Saturday during the Preliminary level round of cross-country at the Red Hills Horse Trials in Florida.