Sources in RTE today told the Herald that Ms O'Callaghan described Mr McGuinness' demeanour at the midnight encounter as threatening and intimidating.
The Herald observed Mr McGuinness ushering the TV host outside into the corridor while she was waiting to speak to reporters.
"Martin McGuinness refused to leave the station without speaking to Miriam over her so-called mistreatment of him during the debate," said an RTE insider.
"It was offered that she would be accompanied into the dressing room but she agreed to go in alone with him. He was extremely angry and intimidating and Miriam was left very shaken."
During the live debate Mr McGuinness accused the presenter of asking "disgraceful" questions.
The drama unfolded following several heated exchanges between the pair over the Sinn Fein man's IRA past.
A spokeswoman for the Aras candidate denied any intimidation.
"If you want my personal view she launched an attack on Martin McGuinness last night. It was not a debate. I wasn't there so at this point I cannot comment on the meeting between the two," she said.
And the Herald can reveal that Sinn Fein today sent out emails to all party members -- urging them to make an official complaint to RTE about their presenter.
When asked about about his involvement in "the murder of so many people", the Sinn Fein politician dismissed Ms O'Callaghan of making a "disgraceful comment".
The broadcaster continued to tackle the former IRA chief about the "horrible murder" of Private Patrick Kelly and told him that it would be incredibly humiliating to the Irish people if someone accused him of murder while at an international event.
A clearly irate Mr McGuinness then attempted to harangue the presenter and accusing of her making "stupid statements".
He then continued to attack the mother-of-eight after the debate, suggesting that her chairmanship was a "disservice" to viewers.
"The focus was on the past and not on me as president and what I would do in the future and I think that was a great disservice to the viewers," he told reporters.
"The greatest disappointment has to be that none of the candidates got a real opportunity to outline their vision of the future, that was the greatest disappointment.
"The big focus was on looking at all of the candidates in relation to the past and that took up the bulk of the show. I think the viewers wanted to hear what's happening in the present and what's happening in the future."
Speaking afterwards, Ms O'Callaghan emphasised that it was her sole intention to ensure the debate was fair and balanced.
"We thought about splitting them but then we couldn't agree on the split. Who would you split people with -- political and non political?
"It wasn't agreed.
"People didn't want to be sitting beside certain people and beside other people on a different night so we thought about it but it's not practical, you can't do that.
She added: "The most important thing about debates is that they are equal and fair which is why we talk about timing them."
Ms O'Callaghan was unavailable for comment when contacted by the Herald today.