Toyota has voiced concerns over the nature of Kazuki Nakajima’s accident that has resulted in the Japanese driver sustaining a fractured vertebra and now highly unlikely to take part in next month’s 24 Hours of Le Mans.

Nakajima ran into the rear of Oliver Jarvis’ No. 8 Audi R18 e-tron quattro in Thursday’s rain-soaked FP1 at Spa-Francorchamps, with Jarvis reported to have been on his out lap and at reduced speed, according to Toyota Gazoo Racing technical director Pascal Vasselon.

“This is a question mark,” Vasselon said. “How can a professional driver be at 160 km/h (100 mph), on the racing line, where others are coming at 285 km/h (177 mph)? The impact was with more of a 100 km/h difference.”

“We saw the on-board video of Kazuki. You don’t see anything until the end. He was catching and passing the No. 7 Audi, which you clearly see.

“In front, you see a sort of grey [mist]. Suddenly, within one-tenth [of a second], you see two red glows. Then the car is then in the windscreen.”

Vasselon’s other concern is the visibility of the tail lights, which Nakajima didn’t see on the Audi until it was too late to react.

“Here it raises one question, which we have already discussed with the FIA and ACO, is the visibility of the rain lights,” he said. “Because clearly this is the kind of accident that should have not happened.

“When you see the other video from the circuit, you see Jarvis slow and Kazuki behind but you cannot see the car.”

Vasselon believes the lack of reaction time contributed to Nakajima’s lower back injury, which was similar in fashion to the fracture Anthony Davidson sustained in his high flying accident at Le Mans in 2012.

He, however, insisted it was a generic issue due to the seating position in all LMP1 cars and nothing specific to Toyota, which has collaborated with the FIA since Davidson’s accident to better understand seating and belt positions.

“The problem is that when you have an impact from the front, they cannot move,” Vasselon explained. “All of the impact is taken by the [spine].

“You have another worsening factor related to the belts because the body of the driver moves and the belt compresses. You have the back, which is blocked by the seat on all cars and you have the belt.

“The [result] is always the same with L4 or L5 [vertebrae fractures]. This is something that’s generic and there are studies ongoing to cure it.”

The accident resulted in the No. 1 Toyota TS040 Hybrid having to be re-tubbed and only returned to action during this afternoon’s dry FP3 with Anthony Davidson and Sebastien Buemi at the wheel.

While the No. 1 car will run with a two-driver lineup in tomorrow’s Six Hours of Spa-Francorchamps, Vasselon said preparations are already being made to put reserve driver Kamui Kobayashi into action.

“We are organizing a test session to get him mileage,” he said “He will be present at Le Mans for sure.

“Kazuki really has a fighting spirit and he wants to give a chance to recover. So he’ll stay in Europe to recover to maximize his chances of recovery [for Le Mans].

“But his chances are very slim and very unlikely. So that’s why we’re getting prepared to replace him. But he doesn’t want to rule it out himself.”