OTTAWA - Outgoing NDP leader Tom Mulcair says it is important for his successor to have a seat in the Commons - an issue playing out in the current battle to replace him.

Ontario legislator Jagmeet Singh is the only contender in the NDP leadership race without a federal seat.

He is running against three sitting MPs: Manitoba's Niki Ashton, Quebec's Guy Caron and Ontario's Charlie Angus.

Mulcair said Tuesday he will let the "only person in the race who's not in the House yet" decide how to proceed but he admitted one option is far better than the alternative.

"I think that if we're going to have somebody leading the party after I'm gone, it'll be a heck of a lot better to have that person crossing swords on a daily basis with the prime minister," he said.

Mulcair's comments come one day after Angus took aim at Singh over the issue, suggesting he does not understand how someone can lack a seat and go on to ask Canadians for a promotion to be prime minister.

"I was surprised that Jagmeet said he didn't think he needed to be in Parliament until 2019," Angus said Monday.

"That's his choice ... my focus is Parliament, what we are going to do there and the building on the ground from that."

It will be up to party members to decide whether they want a leader who can square off right away with Prime Minister Justin Trudeau, and the party has already waited long enough, Angus said.

In April 2016, just six months after the party's disappointing 2015 election result, NDP members rejected the long-term leadership of Mulcair, prompting the current leadership race. He has decided to stay on until his replacement is named.

Singh said Tuesday he is not concerned about his lack of his seat in the Commons, suggesting he will use the time to get to know Canadians and rebuild support for his party.

He also left the door open to running in a byelection prior to seeking a seat in the 2019 election.

"I am confident and comfortable with that current state of affairs and I'm also willing to hear people out," he said in an interview.

"Right now, the area I represent is in Brampton Mississauga. It is an area I've represented for the past six years, where I've knocked doors, where I have the strongest connection ... I'm willing to open other ideas on where it makes sense to run."

Singh has been able to garner the most support from the current federal caucus. B.C. MP Nathan Cullen is expected to endorse him on Wednesday, joining 10 other MPs who have done the same.

Caron has been backed by eight MPs, while Ashton has received nods from five. Angus has been supported by two.

The NDP is set to announce its next leader next month.

The first ballot results will be unveiled in Toronto on Oct. 1 and if a candidate receives more than 50 per cent support, he or she will be named the next leader. Otherwise, a subsequent round of voting will ensue.