Oscar Piastri has a simple request for his Formula One debut: don't judge me.

The Melbourne-born 21-year-old will become the 15th Australian to race a F1 grand prix when the fresh season opens in Bahrain.

Piastri expects mistakes and middling results as he prepares to take to the track in his McLaren for practice sessions starting Friday night (AEDT).

"The first race of my career is not where I'm going to be fighting for wins and podiums," he told reporters in Bahrain.

"I think learning as much as I can is by far the most important thing at the moment."

Piastri enters the F1 paddock with a glistening record: champion in the Formula Renault Eurocup in 2019; champion in Formula 3 in 2020; champion in Formula 2 in 2021.

But he hasn't raced competitively since that F3 title, biding his time as an F1 reserve driver for Alpine last year.

After the F1 season, Piastri was involved in a bitter tug-of-war between Alpine and McLaren for a driver's seat this year - effectively, he signed with McLaren while contracted by Alpine, who later released him.

Piastri was unflappable throughout the controversy which ended with him taking fellow Australian Daniel Ricciardo's seat in a McLaren.

Now, he's similarly calm about his looming debut.

"I have been waiting a long time ... it's great that the moment is finally here," he said.

"It has been a while since I last raced so I'm itching to get going again."

Piastri and his teammate Lando Norris have low expectations for their McLarens, with team hierarchy conceding they're in a development phase.

"We still don't know where exactly we sit," Piastri said.

What would be satisfactory in Bahrain?

"Just coming out of qualifying and the race ... knowing that I have done close to the best that I can, factoring in maybe a few mistakes here and there," he said.

"The race, obviously it's a very different kind of racing to what I have had in the past - and especially for the last year because I haven't had any.

"Going through the race, results aren't necessarily the most important thing.

"I would rather a race where the result is a bit worse but I learned double as much that I can carry into the rest of the season."

The Bahrain race starts 0200 AEDT on Monday.