Businessman Mr Denis O'Brien threatened tonight to take the Moriarty Tribunal to the High Court to prevent further damage to his personal reputation.
Counsel for Mr O'Brien, Mr Eoin McGonigil, said the tribunal's investigations into his client's £4million purchase of Doncaster Rovers Football Club in 1998 was incomprehensible.
The tribunal is investigating the possibility that former Communications Minister Mr Michael Lowry was involved in the deal.
Mr McGonigil said: "There is nothing to suggest that Michael Lowry had any involvement, good, bad or indifferent. It is preposterous (for the tribunal) to damage the reputation (of Mr O'Brien) rather than vindicate the reputation of Mr O'Brien in a proper fashion."
He warned that unless the tribunal looked at the matter properly he would seek an order in the High Court on Friday or Monday to prevent it carrying out its work.
Mr McGonigil criticised the tribunal's delay in dealing with the issue.
Today was its first sitting in five months.
Mr McGonigil said key figures in the Doncaster deal were outside the jurisdiction of the tribunal and had no intention of appearing to give evidence.
He said this included Christopher Vaughan, a Northampton-based solicitor who wrote a letter in September 1998 which alluded to the involvement of Mr Lowry in the deal.
Mr Vaughan has since told the tribunal that he erred in making this assumption.
But Mr McGonigil said despite the tribunal's assertion that Mr Vaughan might give evidence, his stated position was that he would not.
The tribunal has confirmed three other key figures in the deal will not be giving evidence.
They are Mr Ken Richardson, a British businessman who sold shares in Doncaster to Mr O'Brien's company and was later convicted of the arson of Doncaster Stadium in 1999, Mr Kevin Phelan, a Northern Ireland businessman who alerted Mr O'Brien to the deal, and Mr Mark Weaver, an agent for Mr Richardson.
However the tribunal said that allegations against Mr O'Brien by witnesses who refused to substantiate them would not be aired publicly.
Judge Michael Moriarty said the tribunal's deferral since last April had taken much longer than he would have wished.
He said the reasons for this included complying with the recent court decision involving Cork developer Mr Owen O'Callaghan, which found that the Mahon Tribunal should give him all documentation relevant to his case.
He added: "As to the substantive matter mentioned by Mr McGonigil I am far from unaware of aspects of frailty of witnesses of possibly dubious provenance and who are lurking in the background of the matter."
He said the tribunal's verdict on the Doncaster deal might well vindicate Mr O'Brien's position.
But that the evidence had to be heard in public. "In the light of what was made available, it would have been remiss had I not embarked upon consideration of the matter. I will not make a determination until I am satisfied I have heard all the material evidence that pertains to the matter."
The tribunal was adjourned until 11 a.m. next Tuesday when Mr Michael Lowry's accountant, Mr Denis O'Connor, will give evidence about his involvement in the Doncaster deal.
PA