Eleven-time Paralympic gold medallist Dave Roberts has failed to reverse the decision to omit him from the GB swimming team for the London Games.
British Swimming were obliged to reconsider their decision not to select Roberts after he won an appeal in June.
But a review by national performance director John Atkinson has concluded that the original decision will stand.
"It's awful to think that I'll never be able to compete in the Paralympics in Britain, my home nation," said Roberts.
"I fought for the opportunity to be reconsidered tooth and nail, but after months of waiting and hoping, it wasn't enough.
"I'm still not going to compete as part of the team that I've trained with for 14 years."
Roberts missed the first set of GB trials through illness and failed to make the times for the 50m and 100m freestyle at the second trials in Sheffield in April.
He has struggled with illness and injury over the past three years, including a bout of pneumonia earlier this year, and argued those circumstances should have been considered by British Swimming in their selection process.
An appeals panel found in his favour, forcing British Swimming to consider his case for selection under discretionary criteria within their own policy, based around fitness and medical issues.
But chief executive David Sparkes said: "After a robust and independent appeals process, British Swimming followed the recommendations of the independent Appeals Committee and after receiving an independent medical report we believe Dave has not met the standards set out for selection to the Paralympics Games.
"Obviously we are sorry that Dave will not be there and we all wish him well for the future. I am sure that he, along with all of us, wish the whole Paralympic team good luck for the Games."
Roberts, who won four golds in Beijing four years ago, needs one gold to overtake Baroness Tanni Grey-Thompson's medal tally and become the most successful British Paralympian of the modern era.
He added: "Despite not being able to compete in the event that I've been gearing up to for years, this won't necessarily be the end for me.
"I'm still at the top of my game, I feel that I still have medal potential and I will continue to train."