After seven race wins last season and a third-placing in the drivers championship, Piastri has generated huge buzz in his hometown Melbourne and is expected to draw record crowds for his bid to become the first home winner since the race joined Formula 1 in 1985.
McLaren qualified both cars at the front of the grid last year and Lando Norris won the season-opener on a wet track, but Piastri said he had "no idea" whether he could win this year as the team grapples with F1's biggest technical overhaul in decades.
"Based off testing, we seem like we’re in the mix at the front," he said.
"I certainly wouldn't be saying that we're favourite to be winning. The picture doesn't look quite as positive for us at the moment as it did 12 months ago.
"We're in the mix, but we need to find a bit more."
Piastri led last year's championship by 34 points before a mid-season slump opened the door for British teammate Norris to claim his maiden title.
He said the disappointment of missing out had faded and he had little time to dwell on the past due to the short off-season and the need to get up to speed with the technical changes.
He also said he felt no extra burden to perform at his home race, a year after finishing ninth following a skid into grass.
"Obviously last year's race didn't end how I wanted, but you know, there's no extra pressure to try and make up for that or anything," he said.
"We've got enough challenges to not be worrying about that."
Defending champion Norris may again loom as his toughest adversary, even with pre-season buzz surrounding Mercedes and Ferrari following their positive winter testing.
McLaren gave equal treatment to Piastri and Norris last year, although there were controversies involving the application of the team's so-called 'Papaya Rules'.
One involved the Australian letting Norris past after a botched pitstop by the team at Monza.
Piastri said any issues from last season had been dealt with internally and the team had moved on.
"We're not going to be swapping each other around for no reason (when racing)," he said.
"Again, if there's any issues or tense moments that arise, then we'll deal with it as a team, as we do and try to make some progress."