Julian Assange was obviously resorting to publicity stunt when he unveiled his plans to bring up legal charges against Prime Minister Julia Gillard, whom the WikiLeaks founder has accused of defamation.

This according to defamation expert Stuart Littlemore, who insisted that Mr Assange was likely misinformed or uninformed of legal requirements that defamation suits must be filed within 12 months after the subject comments have been made.

"I cannot imagine that there is a cause of action that WikiLeaks could ever bring, least of all if it had done it within time," The Sydney Morning Herald quoted him as saying on Monday.

In an interview with Fairfax Media today, Mr Littlemore, known in Australian legal circle as a skilled litigator in defamation cases, explained that "nobody can sue for something that is statute-barred . . . they would need the leave of the court, and I can't see why that would be granted."

"I can't see that it is anything else but a stunt," the barrister stressed, reacting to an earlier declaration by Mr Assange that he had already hired Sydney lawyers to study the possibility of suing Ms Gillard.

Should a legal case against the prime minister actually prospered, Mr Littlemore said he would be quite happy to defend the Labor leader and the only thing that would prevent him from doing so is being accused of peddling his legal services.

Subject of Mr Assange's likely suit against Ms Gillard was the latter's statement in 2010 condemning WikiLeaks' decision to publish tons of confidential diplomatic documents that were embarrassing on the part of the U.S. government.

"I absolutely condemn the placement of this information on the WikiLeaks website. It's a grossly irresponsible thing to do and an illegal thing to do," the Australian Associated Press (AAP) reported Ms Gillard as saying at that time.

That single statement made by the foremost political figure of Australia prodded credit card company MasterCard to stop facilitating donations that were made through the firm's facilities, Mr Assange said in a video interview with activist group GetUp.

"MasterCard Australia, in justifying why it has made a blockade preventing any Australian MasterCard holder from donating to WikiLeaks, used that statement by Julia Gillard as justification," the controversial whistleblower was quoted by media reports as saying in the video.

He insisted that "the effects of the statement are ongoing and they directly affect the financial viability of WikiLeaks."

Yet according to a statement issued by MasterCard, "the decision to suspend acceptance to WikiLeaks was MasterCard's alone."

"Given the serious nature of the allegations and some of the public comments by senior elected officials from around the world ... we believed it was prudent to suspend acceptance," the credit card firm's statement was reported by ABC as saying on Monday.