Alternatively, he could get a start if Mark Craig's confidence, with figures of 0-156 from 31 overs, is shattered. New Zealand could play four pace bowlers on the fast Waca wicket and bring in left-arm orthodox spinner Mitchell Santner as the all-rounder.
Fulfilling the third pace bowler role is a difficult proposition. Traditional statistics tend not to be a first change's friend because they don't necessarily drill into the detail. They often toil for long spells when the going is tough and shorter spells when the star opening bowlers revel.
Wagner toured England mid-year, but the last of his 16 tests was the Boxing Day match against Sri Lanka. The 29-year-old was ushered out of the squad for the Australian tour, with the selectors opting for two all-rounders in Jimmy Neesham and Corey Anderson. When Anderson was ruled out injured, Santner replaced him.
Rash or knee-jerk decisions are not the custom of this selection panel. They prefer to give players sustained opportunities because of the confidence it can generate. However, the punishment this XI's bowling attack took in Australia's first innings, at what one dag in the press box referred to as the Gabba-toir, might give cause for introspection.
Wagner's most recent first-class outings saw him take eight wickets at an average of 33.5 opening the bowling for New Zealand A against Sri Lanka A in four-dayers at Christchurch and Lincoln.
In his first eight tests, New Zealand didn't win. In his second eight tests, they didn't lose. He has 58 test wickets at an average of 34.48, yet last year produced stellar performances against India in Auckland and the West Indies in Barbados to bowl New Zealand to a couple of series-defining test victories.
He largely bowled in the shadow of Boult and Southee, striving into the wind without a new ball. He fought the teeth of opposition middle orders but got few opportunities to devour their tails. As a result, he doesn't boast a sub-30 average.
Yet in the harsh environment of Australia, where experience can have a major impact, Wagner's tenacity could galvanise the attack.