Honda suspects an Energy Recovery System failure prevented Fernando Alonso's McLaren from starting Formula 1's Russian Grand Prix.
Alonso's nightmare season continued at Sochi as he reported problems with his car over the radio before the start, and then stopped on track before he could even complete the warm-up lap.
It was Alonso's fourth retirement in four races and the second time this season a McLaren has failed to take the start of the race, following his team-mate Stoffel Vandoorne's similar experience in Bahrain a fortnight ago.
"It's sad but nothing I can do now," said Alonso.
"As soon as we started the formation lap we didn't have the normal power.
"They asked me to change a few things on the steering wheel to try to recover the ERS, but there was no way and at the end of the lap the car stopped.
"We couldn't even start the race this time.
"I feel bad. We all wanted to be there but these things happen. This is sport.
"When you are here and you can't race, what can you do? It's not in your hands."
The full details of the problem will not be known until Honda conducts further analysis.
"Until the car is back in the garage they won't have the answer, but it's a power unit problem," Alonso added.
"Let's hope we can solve them as quickly as possible because we haven't finished a race this year and we couldn't even participate in this one, so there's a few things to improve."
Alonso will now shift his focus to Indianapolis, where he is scheduled to make his IndyCar test debut with Andretti Autosport this week.
"I'll see if I can flight an earlier flight but there doesn't appear to be, so I'll watch the race and have an ice cream," Alonso joked.