Paralympian Dave Roberts has had to pull out of the British Gas Swimming Championships 2012 with pneumonia.
Welshman Roberts was diagnosed following a British Swimming training camp in South Africa in January.
"I am disappointed with having to withdraw from the trials due to ill health," said Roberts.
"But I am very confident with British Swimming's ongoing support I will be ready to race in the second trials in April.'
The 31-year-old Caerphilly swimmer, has been receiving treatment, and though he is recovering will not be able to compete at the first part of the Paralympic trials at the Aquatics Centre in London.
An eleven-time paralympic gold medallist, Roberts is one of Great Britain's most successful Paralympians ever along with fellow Welsh athlete Dame Tanni-Grey Thompson.
National Performance Director John Atkinson commented: "Dave has had a tough year.
"He had to miss the IPC European Championships with an arm injury and had successfully got back into full training once that had healed.
"We are supporting Dave in his recovery from pneumonia and our medical team are in regular contact with him.
"The competition came too soon for him to be back to full fitness. We will continue to support Dave on his road back and we hope to see him at the second trials in April."