The 43-year-old former entertainer, whose self-help business boasts clients such as Saatchi and the law firm Freshfields, complains he was "pilloried" by journalist Victor Lewis-Smith on about ten occasions since 1997.
His action against the publishers of the Mirror arises from an October 2003 article, "It's a load of doc and bull", which mentioned his "bogus degree" from Lasalle University, Louisiana.
In it, Lewis-Smith wrote: "I discovered that anyone could be fully doctored by Lasalle within months (no previous qualifications needed), just so long as they could answer the following question correctly: 'Do you have $2,615, sir?'".
McKenna was at the High Court in London to hear his counsel, Desmond Browne, QC, tell Mr Justice Eady - who is hearing the case without a jury because of the paperwork involved - that his case was very simple.
"Victor Lewis-Smith and the Mirror pilloried Mr McKenna as a fraud, claiming that he had a doctorate to which he had no honest entitlement. They can't prove that to be true."
Mr Browne said McKenna was unaware until his course was almost complete, in 1996, that Lasalle was only accredited by a body which turned out to be a fraudulent creation of the university's founder, Thomas Kirk.
But this lack of accreditation did not mean that the university was a diploma mill. He added that McKenna had been an innocent victim of Kirk's fraud.
The hearing continues today.