Phillips is aiming to compete in Kentucky, but not on Toytown
Zara Phillips will not defend her world three-day eventing title aboard Toytown in the USA this autumn.
The combination were crowned 2006 world champions in Germany, a year after landing the European individual title.
But Toytown has since been plagued by a series of injuries, and Phillips said: "There are no plans for him this year."
However, she has not given up hope of gaining Great Britain selection for the World Equestrian Games in Kentucky from 25 September to 10 October.
Toytown is currently doing light training work, and Phillips said: "We are just going quietly with him. He doesn't owe me anything - there is no pressure."
She has entered her 15-year-old Glenbuck for the Badminton Horse Trials, starting on 30 April, in addition to 12-year-old Poilu, which was ridden last year by Australian Clayton Fredericks and is now part of Phillips' 15-strong string of horses.
Realistically, she needs a top 10 Badminton finish to strengthen her selection case for Kentucky.
"It all depends on results," she said. "There are a lot of people out there with good combinations."
Reigning European champion Tina Cook, the 2009 Badminton and Burghley winner Oliver Townend and multi-major event winner William Fox-Pitt appear certainties for Kentucky.
Elsewhere, the likes of Piggy French, Nicola Wilson, Mary King and Lucy Wiegersma also have strong claims, which underlines the size of Phillips' task.