Two-time Paralympic silver medallist Tom Hamer has been forced to withdraw from Tokyo 2020 due to a back injury.
The 23-year-old swimmer claimed second spot in both the S14 200m freestyle and 200m individual medley at Rio 2016.
He had been due to defend the first of those titles on Friday.
British Para Swimming performance director Chris Furber said in a statement: "The team have supported and helped Tom to manage his injury.
"We wanted to give him as long as possible but sadly he's just not able to compete anywhere near his best.
"He has been an integral part of the team and he has pushed everyone on, so we're all sad he isn't able to compete."
