The issue is expected to be raised at the long-awaited crunch meeting, despite reports Mr Ahern will claim he left the country in a strong position when he resigned and did nothing wrong.
In previous evidence to the inquiry, former Department of Finance secretary general Kevin Cardiff confirmed government set up a “secret” group to examine a bank guarantee as early as autumn 2007.
Ex-taoiseach Brian Cowen subsequently confirmed the situation, while also saying the “soft landing” theory pushed by Mr Ahern was not based on any government analysis and that a guarantee was genuinely considered from “April or May” 2008.
As a result of the issues, Mr Ahern is likely to be grilled on how much he knew before being leaving office in May 2008.
However, leaks of the former Fianna Fáil leader’s evidence shows he is due to make a staunch defence of his time in power and insist he left the country in better shape than when he became taoiseach.
His appearance will take centre stage in two days of evidence which will focus on what exactly Mr Ahern knew about Ireland’s financial help, the legal advice given and whether banks withheld information as the boom went bust.
Today, the inquiry will hear from former NTMA chief executive John Corrigan, former Irish Banking Federation chief executive Pat Farrell and ex-Department of the Taoiseach secretary general Dermot McCarthy.
Also tomorrow, the inquiry will also hear from former attorney general Paul Gallagher and Arthur Cox legal representatives.