Racing Point has confirmed a clutch bolt issue prevented the team from being able to fire up Nico Hulkenberg's engine, ruling him out of the Formula 1 British Grand Prix.
Hulkenberg was drafted in at the 11th hour to replace Sergio Perez, who tested positive for COVID-19 on Thursday.
Qualifying 13th for his first race since Abu Dhabi 2019, Hulkenberg was unable to take the start when Racing Point was unable to fire up his car, with investigations revealing a clutch bolt had failed and come loose within the drivetrain.
"It looks like a bolt sheared within the clutch housing," said team boss Otmar Szafnauer.
"And that bolt got caught and therefore wouldn't allow the internal combustion engine to turn over.
"So where the bolt fell off, it got jammed, and we couldn't turn the engine over.
"I think it's a bit early to understand why, but it did shear off so it could be a material issue, it could be an over-torque issue, I don't know.
"I'm sure all of those bolts are torqued to a certain specification, say the torque ratio isn't set right and you over-torque it, it could shear it.
"It could be a material issue in manufacturing, but until you look into all of those things - was the bolt brittle for example, I don't know - so we'll have to understand the root cause and make sure we fix it."
Szafnauer confirmed that the bolt was part of the package provided by Mercedes.
"It's not a Racing Point part, that's a part we get from either HPP [High Performance Powertrains] or MGP."
Szafnauer admitted that Hulkenberg's failure to start was hugely frustrating, especially as he'd got up to speed so well after jumping into the car on Friday.
"It would have been very useful for Nico to get a race in," he said when asked by Autosport.
"Unfortunately he didn't. I think he did a great job jumping in the deep end, starting from zero really, he didn't do any winter testing, didn't understand the car at all, it's a different car than he drove before, a different powertrain.
"The team is similar to when he was here, but he still had a different engineer as his old engineer is on Lance's car, but the rest of the guys he worked closely with, so he did a remarkable job.
"It was a steep learning curve, he did great to qualify where he did and it's a shame he didn't get to race."