“Sadly @lorenzo99 has been declared unfit for the remainder of the #DutchGP,” Honda tweeted.

Lorenzo slid out at turn seven of the Assen track, bouncing into four somersaults as he hit the gravel behind his bike.

Two doctors were quickly at his side and helped him walk gingerly off to the barriers before he sat down and was then taken away to the medical centre by ambulance.

Michele Zasa of Clinica Mobile told motogp.com: “Jorge reported on the CT scan a fracture on the 6th thoracic vertebrae, so they are still deciding how to proceed.

“For sure he’s unfit, for the moment, there is this reported fracture on the 6th thoracic vertebra …

“He moves everything and doesn’t have any neurological signs. Now we will see how to proceed for the next hour and what the treatment will be.

“The helmet has external signs like scratches but he didn’t lose consciousness, he was okay, not knocked out or concussed. So, the contusion was to the chest and the back.”

Loreanzo will be repatriated to Barcelona later Friday for more tests.

The 32-year-old Spaniard has struggled early in the season after joining Honda from Ducati.

He currently lies 15th in the championships standings with 19 points, his best performance an 11th placed finish at the French MotoGP.

Yamaha’s Maverick Vinales topped the timesheets in the first two practice sessions with a best lap of 1min 32.638sec.

He shaded another Yamaha of Fabio Quartaro by 0.180sec with Ducati duo Danilo Petrucci and Andrea Dovizioso in third and fourth, and championship leader Marc Marquez back in seventh at 0.775.