Outgoing NDP MP and former party leader Tom Mulcair is wrapping up his political career with some words of warning for his party after its disappointing third-place finish in a Quebec by-election:

Start worrying now.

"I am worried about a score like that, what it means for the future, no doubt," Mulcair told host Vassy Kapelos on CBC News Network's Power & Politics.

The NDP vote suffered an almost total collapse in the Chicoutimi-Le Fjord, Que. byelection on June 18. The party pulled just 8.7 per cent of the vote — after winning the riding with 37.7 per cent in 2011 and narrowly losing in 2015 with 29.7 per cent of the vote.

Mulcair called the result "an outward sign that there's still a lot of things that have to be done differently" by the party before the 2019 federal election.

NDP Leader Jagmeet Singh shares his predecessor's concerns; this week he called the results "disappointing" but added he believes last year's NDP leadership race was a factor in this week's by-election result.

"We had a period of time where we had a leadership race, and that takes away from your ability to have a clear leadership in directing the work," Singh said.

Singh 'does have a great personality'

In his interview with Power & Politics, Mulcair credited the NDP's dominance in Quebec in 2011 to "five years of tireless work across the province" and suggested the party — and specifically Singh — need to make the same sort of effort now.

"Quebecers need something concrete. Not something vague": Former NDP Leader Thomas Mulcair tells Power & Politics after a disappointing byelection result. 7:30

"He does have a great personality and he does connect well with people, but it's a question of time spent," said Mulcair.

"Quebeckers need something concrete and not something that's sent in from another place."

Singh currently does not hold a seat in the House of Commons.

Mulcair added that while the NDP still has more federal seats in Quebec than the Conservatives and Bloc Quebecois, "more work on the fundraising front" will be required ahead of 2019.

But first, there will be a byelection in his own riding of Outremont in Montreal, where Mulcair is predicting a "tough fight" once he departs in a few weeks.

"It's a very diverse riding and you've got to be able to connect in all those different areas," he said. "I'm going on to [teach] university and will be taking a little bit of a back seat, but it doesn't mean I won't be following with great interest."

Mulcair will start working as a visiting professor in the political science department at Université de Montréal this summer.