The 28-year-old, who is the daughter of eventing legend Lucinda Green, was on site at the event with her 15-year-old ride Malin Head Clover, known at home as Ali G, when she broke the news that he was going to be unable to compete.
She posted on her Instagram page shortly before the first horse inspection was due to get under way: “Sadly I have had to withdraw MALIN HEAD CLOVER (Ali G) from Burghley Horse Trials."
“I am in total shock, he has felt brilliant in this whole lead up, he was sound this morning on our wonderful ride together through Burghley Park and now, for whatever reason, he is not.
“I have no idea why or how this has happened – it could be anything from a bang in the stable to something in his foot to God knows what. Although not immediately obvious, it is there and I can’t risk competing my beloved boy in this condition.”