Ian Thorpe said his reputation had been permanently tarnished by the leaking of a report saying he was under investigation for a doping test.
Although doping and swimming officials have confirmed there is no suggestion that he failed the test, Thorpe said the damage had already been done.
"I am deeply alarmed that information about my test result was leaked to the press before I was informed of it," the Australian said in a statement on Sunday.
"The press receiving this information before an athlete jeopardises the whole integrity of the testing process."
Thorpe said the publication of his name was a breach of his privacy and the basic principles of justice.
"The obligations of confidentiality that are owed to me under the WADA (World Anti-Doping Agency) Code are meant to protect the reputations of innocent people from being damaged by media speculation while the routine results management processes are being undertaken," he said.
"I have been deprived of this protection by the deliberate act of the person who leaked this information."
Thorpe's lawyer Tony O'Reilly said legal action would be taken.
"The breach of confidentiality is a very stark one," O'Reilly told a news conference.
"These provisions are in the code to protect people when these routine processes are going on.
"They're there to stop this sort of media speculation that damages
LONG-TERM IMPLICATIONS
Thorpe said he was confident he would be cleared of any wrongdoing but was concerned about the long-term implications and the breakdown in protocol.
"This is a serious issue not only to me but to all athletes," he said.
"We put a lot of confidence into this testing procedure and to know that information can be leaked is a serious breach of what we sign up for.
"It will have to be addressed not only in my sport but all sports that we commit to making sure that the procedure of the testing process is better than what it is now."
Thorpe, who retired from swimming last year, said he did not know who was responsible for the leak but was suspicious that it coincided with the world championships in Australia.
"I don't think it was a coincidence that it happened here," he said.
"You would have to question the personality of the person who would do something like this."
Thorpe was an outspoken critic of the procedures used by the sport's world governing body FINA to catch drug cheats and his comments once landed him in hot water.
He was reprimanded by FINA for bringing the sport into disrepute after claiming it was naive to think all swimmers at the Athens Olympics were drug free.