Both Piastri and teammate Lando Norris failed to start the Chinese Grand Prix, with separate issues stopping their cars from reaching the grid for lights out.
The terminal failure made Piastri the first McLaren driver in 57 years to fail to start two consecutive races, after the Australian crashed out on the way to grid in Melbourne last week.
McLaren are one of several teams who do not have their own engine supplier, instead holding a deal with Mercedes whose works team have dominated the opening two rounds.
Engineers were on Sunday night still trying to determine the root causes of Piastri and Norris' issues, which they believe came in the same electrical component of the power unit.
"It's quite exceptional and uncharacteristic that you have two terminal problems, pretty much at the same time on the same component," team principal Andrea Stella told reporters.
"Obviously this is an area of the car which is not under McLaren's control, so we rely entirely on what is reported by HPP (Mercedes High Performance Powertrains).
"And according to their report the two problems are of a different nature ... We will review together with HPP the reason for these faults."
Stella had noted after last week's Australian GP that McLaren for the first time felt "on the back foot" with their power units this year, only making key learnings in pre-season testing.
For Piastri, his miserable start to the campaign may serve as a reminder of the opportunity he missed last year when leading the championship for 15 consecutive rounds.
While McLaren were by far the fastest car last season as Norris snatched the title, they are now clearly behind both Mercedes and Ferrari under the 2026 regulations overhaul.
McLaren have brought the best mid-season upgrades of all teams in recent years, but none are likely for Japan in a fortnight.
The month-long break after that, caused by the cancellation of races in Bahrain and Saudi Arabia, could play into their favour with time to focus on the cars.
Piastri finished sixth in the Chinese sprint race on Saturday and is now 12th in the championship, 48 points behind leader George Russell.
Norris is also 36 points back, with Russell and teammate Kimi Antonelli having finished one-two in the first two grands prix after the latter's victory in Shanghai.
"It is a tough moment, that is for sure. Oscar has not been able to start a (grand prix) in this 2026 campaign," Stella said.
"That is pretty difficult for Oscar to process.
"But at the same time, and this was witnessed in the conversation with Lando and Oscar after the race, both remain quite positive."
