Under pressure Alasdair McDonnell is expected to face a challenge for leadership of the SDLP.
Colum Eastwood, a former Mayor of Derry and Foyle MLA has been nominated as a contender for the contest which will take place at the party's annual conference in November.
Nominations closed at 5pm and it is understood Mr Eastwood has secured the necessary support from at least five branches.
Although he has declined to comment publicly, sources close to Mr Eastwood said he would be carefully considering the nomination over the coming days.
One senior party source said: "Alasdair was always going to face a leadership challenge. He has been asked to go gracefully and not so gracefully but he has refused to budge."
An attempt to oust a sitting party leader is highly unusual for the SDLP.
Mr Eastwood became Derry's youngest ever Mayor in 2010 at the age of 27.
A year later, he was elected to the Northern Ireland Assembly and sits on the scrutiny committees of the Office of First and Deputy First Minister and the environment.
He was also private secretary to former environment minister Alex Attwood.
The senior source added: "Colum is a great speaker; politically astute and has untapped potential. He is the face of a new generation and will be able to bring energy and enthusiasm to the party.
"A new generation, born after the signing of the Good Friday Agreement (in 1998), will soon be casting their first vote. They have no experience of the conflict and they want to hear something different."
It is believed no other potential candidates have been put forward.
Dr McDonnell, who has led the party since 2011, has recently been forced to bat away stinging criticism from SDLP grandees Brid Rodgers and Seamus Mallon as well as from MP Mark Durkhan,
And, the timing of revelations about a potential leadership challenge fell on another difficult day.
He has faced a barrage of criticism after accusing the Democratic Unionist Party (DUP) of not wanting to work with Catholics.
Dr McDonnell was recorded by the North Belfast News at the opening of a new constituency office in Glengormley, Co Antrim.
The South Belfast MP said: "The DUP don't want partnership - they don't want a taig (derogatory term for Catholics) about the place. I'm sorry, it's as brutal as that.
"I'm not divisive, I don't like to be like that, but at times they've made it very clear to us they don't support the Good Friday Agreement, they don't support a lot of the changes that have taken place."
The controversial comments came at the end of a week of intensive cross party negotiations to save the ailing powersharing Assembly.
The DUP has robustly rejected alleg ations of sectarianism.
MP Jeffrey Donaldson hit back, saying the SDLP leader was "rabble rousing".
He said: "Not only would we reject the allegations that Alasdair McDonnell has made, we would challenge him with sectarianism. To use a deeply offensive term such as 'taig' in a speech is beneath contempt and demeans the office that he holds as leader of the SDLP.
"Instead of rabble rousing in North Belfast, he would do well to be at Stormont with the rest of the political parties to resolve the issues."
The fragile political institutions at Stormont, already under threat of collapse because of the failure to agree a budget, have been rocked by the murder of IRA man Kevin McGuigan last month.
The father-of-nine was gunned down in the staunchly republican Short Strand area in what police believe was a revenge attack for the shooting of one-time IRA associate and former commander Gerard "Jock" Davison three months earlier.
Police said individual members of the IRA were involved in Mr McGuigan's murder, piling pressure on Sinn Fein to explain how the supposedly defunct terror group still exists.
Unioinists have pulled out all but one minister from the five-party mandatory coalition Executive.
Sinn Fein has insisted the IRA has gone away.
However, Dr McDonnell said: "Sinn Fein can't tell the truth. They just can't tell the truth, and they can tell us whatever they like and you've examples like Gerry Adams was never in the IRA and you've examples like Martin McGuinness saying this, that and the other thing. They're not telling the truth."
South Belfast MLA Alex Maskey said the SDLP leader was exploiting the murders for political gain.
He said: "Sinn Fein has repeatedly challenged the SDLP to either put up or shut up, and if Alasdair McDonnell or any other member of the SDLP has any information on the murders of Gerard Davison or Kevin McGuigan, then they should bring that to the police."
Dr McDonnell has not yet fully explained his remarks, but in a statement to the BBC he claimed DUP Acting First Minister Arlene Foster had been disrespectful to nationalists in a recent interview.
Ms Foster has temporarily replaced Peter Robinson while the talks takes place. As the only DUP minister in the Executive she has described her role as a "gatekeeper" against the possibility of decisions being taken by "rogue" or "renegade" ministers.
Dr McDonnell should say sorry, Ms Foster said.
"Alasdair McDonnell should apologise today, not just for an inaccurate slur on the DUP, but for the offence he will undoubtedly have caused to many Catholics by referring to them as 'taigs'.
"Had any other elected representative used such language, they would have stepped forward to apologise."
Meanwhile, South Belfast MLA Fearghal McKinney is also expected to make a bid for the deputy leader's post.
The former news anchorman replaced Connall McDevitt who stood down in 2013 and sits on a number of Stormont scrutiny committees including health and justice.
Mr McKinney is a close ally of Dr McDonnell.
Like the leadership contender, he has to secure nominations from at least five local branches.
The SDLP confirmed the leadership developments.
A party spokesman said: "Two candidates Alasdair McDonnell and Colum Eastwood have been nominated for Party Leader.
"Applicants must be members of the Parliamentary Assembly Group and must be nominated by at least five branches.
"The candidates will now decide if they will accept the nominations.
"Two people Dolores Kelly and Fearghal McKinney have been nominated for Deputy Leader. The same rules apply."