Today has been a “tough day” for Fianna Fáil, Taoiseach (Irish prime minister) Micheál Martin has said.

He was speaking after the party’s candidate Jim Gavin announced he was withdrawing from the Irish presidential election with “immediate effect”.

The taoiseach said despite Fianna Fáil now having no candidate in the presidential vote, his intention is to lead the party into the next election.

Gavin, the former Dublin gaelic football manager was set to be one of three candidates standing for election on 24 October, alongside Independent TD Catherine Connolly and Fine Gael’s Heather Humphreys.

However, on Sunday evening he said in a statement he had “made a mistake that was not in keeping with my character and the standards I set myself”.

Gavin did not elaborate on the reason for his withdrawal in his statement but it followed a news report in the Irish Independent newspaper on Saturday alleging he owed €3,300 (£2,870) to a former tenant.

“This is a tough day for us as a party, it’s not something I anticipated or wanted, in any shape or form,” Martin told Irish broadcaster RTÉ’s Six One programme.

The taoiseach said the party knew previously Gavin used to be a landlord but they did not know about the allegation by a previous tenant that Gavin had not returned him money after it was mistakenly paid.

Martin said at the start of the campaign, there was a “very strong positive reaction” to Gavin and the parliamentary party voted to back him.

He said Gavin was a “broad base candidate”.

“To come off a ticket like this is a momentous decision,” he said.

The taoiseach said Gavin made the decision himself to withdraw from the race.

Asked about owing money to a tenant on RTÉ’s presidential debate on Sunday, Gavin said: “If it happened, I’m very sorry that it happened. I’m looking into it and I will deal with it with urgency.”

It is understood that Fianna Fáil will hold a parliamentary party meeting on Wednesday evening.

Billy Kelleher, who contested Gavin for the nomination, said the party did not do its “due diligence” or “enough of an interrogation”.

Minister for Children, Disability and Equality Norma Foley of Fianna Fáil said Gavin had been right to withdraw.

“I think it was the correct thing to do at this point to withdraw, to stand aside, notwithstanding that it’s really difficult for Fianna Fáil membership, given that we don’t now have a candidate contesting the presidential election,” she said.

Foley added that if Gavin owed money “it must be paid back, there’s absolutely no question about that”.

Her party colleague, Cork North Central TD Pádraig O’Sullivan, said it was “embarrassing” for the party.

“I just believe where we are now, there has to be collective responsibility here,” he said.

Kelleher said the announcement on Sunday evening was a “shell shock” to the presidential election campaign and Fianna Fáil.

He told RTÉ’s Morning Ireland on Monday that it could not “just be swept under the carpet”, adding that Fianna Fáil members and voters across the country were “upset”.

He said he had raised the issue of due diligence “at the outset”, he said.

“I was clearly concerned that there seemed to be no proper process in place, there was no scrutiny of candidates, names were being mentioned on an ad-hoc basis and I just thought, all in all, it was quite a chaotic scene in early August.”

On a visit to Belfast on Monday, Irish presidential candidate Heather Humphreys paid tribute to Jim Gavin.

She said he gave a huge amount of service to the public and wished him and his family well.

But Humphreys said it is “too early” to say if she is now seeking the Fianna Fáil vote.

“I am focused on getting elected and getting my message out to as many as I can.”

She said she wants to “reach out the hand of friendship” during her campaign across communities.

“I want votes from everybody. I want people to vote for me based on my track record.”

Humphreys did not answer a question on whether she would now seek a meeting with the Fianna Fáil leader in a bid to seek the party’s backing for the election.

The Fine Gael backed candidate was speaking at St Dominic’s Grammar School on the Falls Road on Monday.

She said even though people in Northern Ireland cannot vote for her, she came to the Belfast school because former President Mary McAleese is a past pupil.

Gavin is a former Irish military pilot and a current aviation expert but he is best known for his successes as a Gaelic Athletic Association (GAA) football manager.

He managed the Dublin men’s team from 2012 to 2019, when it won six All Ireland Senior Football Championship titles – five of which were back-to-back victories.

He had 20-year career in the Irish Air Corps and was later appointed as Chief Operations Officer of the Irish Aviation Authority.

Last month, Gavin said he had sent legal letters to some social media firms after “smears” of a “very personal nature” were posted about him online.

He said online misinformation had “become normalised” in society and he was “going to make a stand” by contacting media regulators and social media platforms.

Fianna Fáil deputy leader and director of elections Jack Chambers said there had been “extensive and robust due diligence right through the weeks prior to (Gavin’s) candidacy and during his candidacy” but the issue of the tenancy “was never disclosed”.

Chambers said that on Thursday Fianna Fáil received a query to its press office about the issue and the party replied on Friday “following engagement with Jim”.

“At the time he (Gavin) said he had no record or recollection of the particular issue that was set out in the (Irish Independent’s) article on the Saturday,” he said.

“Subsequently on Saturday, the tenant in question contacted the party and said they did have records relating to this particular issue and it was contrary to what the party had been told on Friday.”

He said there is a “full and democratic process” for nominations in the party.

“Obviously there’ll be a meeting, as there always is, of the parliamentary party, and we’ll discuss this matter and discuss the campaign,” he added.

Presidential candidates Catherine Connolly and Heather Humphreys both wished Gavin well following his decision to withdraw.

Connolly said: “Anyone who seeks to make Ireland a better place through public service should be commended.

“Jim Gavin has made the right decision for himself and his family. I wish him well.”

Humphreys added that Gavin had made “an enormous contribution to our country”.

“While I know this must have been a very difficult decision, it is clearly one Jim has made with the best interests of his family at heart.”

Gabija Gataveckaite, BBC News NI Dublin correspondent, answers your questions.

In short, yes. It is too late now to change the ballot under Irish laws. This means three names – Gavin, Humphreys and Connolly – will appear on the ballot.

“Under the legislation this is a matter, in the first instance, for the Department of Housing and the presidential returning officer,” said a spokesperson for the Irish Electoral Commission.

One source with knowledge of Irish electoral laws said “the ship has sailed” to take Gavin’s name off the ballot.

Yes. Gavin’s name will be on the ballot and so technically, even though there is no campaign anymore, he could still win the election. His votes will be counted as usual.

However, it is very unlikely that he would win. The Humphreys campaign will now attempt to shore up as many supporters of Gavin as possible.

Not at this stage. It is too late now to change the ballot paper. The deadline for all candidates was noon on 24 September.

It’s a good question – and it is one for party leader and taoiseach Micheál Martin.

The party will have to decide who, if anybody, they will back in the election now.

The Fianna Fáil parliamentary party is scheduled to meet on Wednesday night.

Votes can be transferred under the Irish system which uses proportional representation. Gavin and Humphreys would be viewed to be very transfer friendly towards one another.

The deadline for voters to register for the election is Tuesday 7 October.