Eight-time Paralympic champion Sophie Christiansen has been withdrawn from Great Britain's equestrian team for Tokyo due to a "minor veterinary issue" with her horse Innuendo III.
The 33-year-old will be replaced by 2019 European gold medallist Georgia Wilson, who will make her Games debut riding seven-year-old mare Sakura in the grade two division.
Wilson, 25, completes a four-person squad already containing reigning Paralympic gold medallists Sir Lee Pearson, Natasha Baker and Sophie Wells.
British Equestrian performance director Richard Waygood said in a statement: "This will be a personal disappointment to Sophie Christiansen, who has worked so hard for a chance to represent her country at her fifth consecutive Games.
"However, with the experience of Natasha, Lee and Sophie now joined by Georgia, who, having tasted medal success in 2019, is ready for more, the British quartet will pose a strong challenge on the Paralympic stage."
Britain has topped the equestrian medal table at the past six Paralympics.
Christiansen – who has cerebral palsy – contributed 10 medals across the last four Games, including three golds at both London 2012 and Rio 2016 following two in Beijing in 2008.
ParalympicsGB Chef de Mission Penny Briscoe said: "This is clearly desperately disappointing news for Sophie who is an incredible athlete, ambassador and advocate for the Paralympic movement.
"An injury to either rider or horse so close to the Games is very unfortunate and we will work with British Equestrian to ensure Sophie has the support she needs.
"Georgia's selection clearly demonstrates the strength in depth in British Para dressage and we are excited to see her make her Paralympics debut in Tokyo."
