Deputy Premier John Barilaro appeared to slip up on Wednesday when explaining that Saturday's poll was not a "proxy three-cornered contest" because independent candidate Joe McGirr was not a de facto Nationals candidate.

"Dr McGirr is not a Nat, he may claim to be, he would love to have run as a Nat but he's not a Nat, he's an independent - and once he gets elected he will sit there on the crossbench with the rest of the independents," Mr Barilaro told reporters in Sydney.

The Nationals aren't running a candidate in Wagga and are meant to be supporting Liberal candidate Julia Ham.

However, party sources have been saying privately for weeks the coalition is at risk of losing the seat on Saturday to Dr McGirr.

Mr Barilaro admitted on Wednesday that some local National members would probably be handing out how-to-vote cards for the independent candidate.

"There'll be National Party members on the ground in Wagga Wagga that would be upset with me, as the leader, that we're not running a three-corner contest and this is their way of expressing those feelings," he said.

Mr Barilaro defended the decision not to run a candidate against the Liberal and Labor parties on Saturday but said the Nationals would reassess their position if the coalition lost the seat.

"If the voters of Wagga dismiss a Liberal candidate this weekend ... well that strengthens my position that the Nats would run in 2019 (at the general election)," he said.

He denied that amounted to an invitation for local Nationals to sabotage the Liberal Party's chances.

"The worst thing that could happen to the government today is the loss of the seat in Wagga Wagga because it actually stops the momentum of regional NSW," the deputy premier said.

"We need to win on Saturday."

Australian Associated Press