Ott Tanak has retired his Toyota Yaris from the lead of Rally GB on Saturday afternoon, allowing World Rally Championship title rival Sebastien Ogier to assume the top spot.
Toyota driver Tanak had been leading the event by 41.9s from Ogier and looked in total control as he headed towards a fourth consecutive WRC rally win, despite a hefty off in shakedown before the event.
But on the Sweet Lamb Hafren stage, SS16, the Estonian pulled off to the side of the road.
After investigating and then removing his helmet, Tanak then drove the car up an escape road before exiting the cockpit again.
Live WRC pictures showed him laying on the floor as co-driver Martin Jarveoja attempted to console him.
Toyota Gazoo Racing boss Tommi Makinen told WRC All Live that the team were unsure of the issue.
"They don't know exactly what happened," he said.
"The sump guard is broken and also radiator but we don't know yet.
"I think he first lost sump guard and then broke the radiator, water pressure is gone.
"It was such a good chance to go well and he was so good through all the stages. It is a big disappointment."
Tanak's retirement means the top four are now split by under 15 seconds, with Ogier leading the remaining Toyotas of Esapekka Lappi and Jari-Matti Latvala, and the top Citroen of Craig Breen.
WRC title leader Thierry Neuville - who entered the event 13 points ahead of Tanak - had been second to the Toyota driver on Friday morning but made a mistake on SS11, dropping him down to ninth until Tanak's retirement.
If the result remains as it is now, Ogier would lie just 2 points behind Neuville, with Tanak a further 15 behind.
Tanak could rejoin tomorrow to contest the five points on offer for the fastest time through the Power Stage, although this has yet to be confirmed by the team.
|1||Sebastien Ogier, J.Ingrassia||M-Sport Ford WRT||Ford||2h13m48.3s|
|2||Jari-Matti Latvala, M.Anttila||Toyota Gazoo Racing WRT||Toyota||5.5s|
|3||Esapekka Lappi, J.Ferm||Toyota Gazoo Racing WRT||Toyota||10.8s|
|4||Craig Breen, S.Martin||Citroen Total Abu Dhabi WRT||Citroen||14.4s|
|5||Mads Ostberg, T.Eriksen||Citroen Total Abu Dhabi WRT||Citroen||31.0s|
|6||Andreas Mikkelsen, A.Jager||Hyundai Shell Mobis WRT||Hyundai||42.6s|
|7||Hayden Paddon, S.Marshall||Hyundai Shell Mobis WRT||Hyundai||45.6s|
|8||Thierry Neuville, N.Gilsoul||Hyundai Shell Mobis WRT||Hyundai||53.6s|
|9||Ott Tanak, M.Jarveoja||Toyota Gazoo Racing WRT||Toyota||6m15.5s|
|10||Kalle Rovanpera, J.Halttunen||Skoda Motorsport II||Skoda||6m29.4s|