Opposition Leader Bill Shorten concedes Labor is facing an uphill battle to retain the federal Melbourne seat of Batman, but says there's already one "loser" in the race.
ALP candidate Ged Kearney and the Greens' Alex Bhathal are frontrunners in Saturday's by-election. The Liberal and Nationals parties did not field a contender.
"The fact that (Malcolm) Turnbull chose not to run makes it harder for Labor to win, because there will be some Liberal voters who will just stay at home and won't allocate preferences ... there's already one loser," Mr Shorten told reporters on Tuesday.
But Mr Shorten later told Sky News the Labor Party was giving it their best shot and he was proud of Ms Kearney's campaign, regardless of Saturday's outcome.
"Malcolm Turnbull has lost Batman because if he had run, he would have gotten a lower vote than he would have otherwise got at the last election," Mr Shorten said.
"There's already one loser out of it and I'm very happy with the campaign that Ged has run, albeit it's an uphill battle."
He said the Liberal Party's decision not to run in the seat made it harder for Labor to win, as many Liberal supporters would not vote or allocate preferences.
Greens candidate Alex Bhathal told reporters in Northcote it's a tight race and she doesn't "take anything for granted".
She said aside from the proposed Queensland coalmine Adani, transport, education, affordable housing to health, were the most pressing issues in the electorate.