The Caterham Formula 1 team is unsure what caused the fuel leak that led to Kamui Kobayashi's car catching fire during free practice for the German Grand Prix.
The Japanese driver's afternoon session came to an abrupt end when he slowed exiting the Sachskurve with flames flicking from the engine bay.
Caterham said a fuel leak caused the fire, but engine supplier Renault is still investigating the source of the leak.
Renault head of track operations Remi Taffin said: "What we are sure of is we had fuel burning on the [engine] cover, which is what you've seen on TV.
"At the moment we don't know where this leak came from.
"We are trying to find out, but when the car is burnt it becomes difficult to find out what happened.
"We've already experienced a few fires like that and it's an unfortunate consequence.
"Fortunately it was an engine that was end-of-life so it's not the big disaster it would have been if it was a fresh engine."
The team has cleaned up Kobayashi's chassis, and he will revert to the engine he raced at Silverstone for the rest of the weekend.
"I smelled something coming out of the hairpin, Turn 6, then in the last sector I lost brakes, lost power, tried to come back, but in the end I couldn't come back so I tried to park close to a fire extinguisher," he told AUTOSPORT, having also helped marshals tackle the blaze.
"I could see the flames in my mirrors - it wasn't very nice.
"The guy [marshal] was not putting any fire extinguishant to the fire itself, just on the bodywork, and the fire would never stop with that, so I needed to help them.
"Not what you need on a hot day - it was too hot already."