Triple Olympic rowing gold medallist Pete Reed is paralysed from below his chest after suffering a spinal stroke.
Reed, 38, won gold at three successive Olympic Games - Beijing 2008, London 2012 and Rio 2016 - as well as at five World Rowing Championships.
He had been training for the Tokyo Games in 2020 but retired in 2018.
"There is a very small chance I will make no recovery and a very small chance I will make a full recovery," he said in a post on Instagram.
"Much more likely it will be somewhere in between. To what extent depends on the extent of the damage (which we can't see) and how well I rehab."
A spinal stroke is a disruption in the blood supply to the spinal cord and Reed says doctors do not know what caused his.
"It was in the middle of my spine so I'm currently paralysed beneath my chest," he added.
"My arms are still strong and my brain is still as average as it ever was."