It will be early next year before the Banking Inquiry delivers its final report, as the committee is now seeking a two-month extension.
The move comes as Alan Ahearne, economist and adviser to former finance minister Brian Lenihan at the height of the crisis,gives evidence at the inquiry.
Other giving evidence today include Alan Gray, former board member, Central Bank of Ireland; and a number of PwC executives.
The 11-person committee had been due to report its findings on November 30, but inquiry chairman Ciaran Lynch has confirmed it is likely to be late January 2016 before the inquiry's work is complete.
Mr Lynch said Senior Counsel Senan Allen's investigation into allegations of wrongdoing at the Banking Inquiry made by a whistleblower has had "an implication" for their work as they facilitated the barrister's probe.
"It did have operational difficulties for the inquiry. That may require further time for the inquiry to complete its work in order to deal with the time that was lost in accommodating the investigation," Mr Lynch told the Irish Independent.
A source close to the inquiry said this was likely to have an impact on the budget for the inquiry, which is believed to be in the region of €5m.
"There has been no formal figure issued by the banking inquiry. "Accommodating the Senan Allen investigation has had implications both in terms of the committee schedule and its costs," the senior source said last night.
Mr Allen's independent investigation, the findings of which were published last week, exonerated the inquiry of any wrongdoing and branded the whistleblower as "a wholly unreliable historian".
Mr Allen was appointed to lead the investigation in July this year, but he concluded last week that none of the inquiry's participants sought "favourable treatment", as had been alleged.
The barrister also said that "robust" procedures, which were in place to deal with conflicts of interest, were "correctly applied".
His detailed report said that allegations made be the whistleblower contained a "good deal of suspicion, surmise and conclusion", but little by way of "hard information".
Members of the Banking Inquiry agreed to seek the extension yesterday. It is understood Mr Lynch will formally make the request on September 22 when the Dáil returns from its summer break.
However, Senator Marc MacSharry remains critical of the inquiry and has contacted the committee again to raise what he describes as "serious concerns".
The Fianna Fáil Senator said he was "uncomfortable with the nature and extent of the review of the disclosure that has taken place."
"My preference before and now is for a full independent investigation that is outside and totally removed from the Oireachtas service," he said.