MotoGP world champion Jorge Martin has been ruled out of the remaining pre-season testing in Malaysia and will undergo surgery in Europe after crashing badly on the opening day at the Sepang track.

The Spaniard broke his hand and foot after being thrown off his Aprilia machine at turn two of the Sepang circuit. He had emerged unscathed from a crash earlier in the day.

He now faces a race against time to be fit for the start of his title defence in the season-opening Thailand Grand Prix on March 2.

"Jorge Martin has been diagnosed with a right hand fracture and fractures in his left foot," MotoGP organisers said in a statement. "He has undergone a CT scan and Magnetic Resonance Imaging (MRI), both of which were negative for any injuries."

"He will stay in hospital overnight and tomorrow he will fly back to Europe to undergo surgery on his right hand and left foot."

The 27-year-old, who made the move to Aprilia after winning the 2024 championship for Pramac Ducati, had completed 13 laps when he lost control of his new bike and was flipped high into the air.

The Spaniard landed hard on his left foot before his head banged onto the asphalt.

Massimo Rivola, Principal of Aprilia Racing, said he had "no explanation" for the crash and that Martin had made "no mistake".

"It was a bad crash with apparently no reason from his side and from the bike," he said. "He is a world champion, but he is also a MotoGP rider. He's not an amateur. And the bike had no problems."

Trackhouse team rider Raul Fernandez of Spain was also ruled out of the remaining two days with hand and foot fractures.

Frenchman Fabio Quartararo, meanwhile, topped the timesheets on the opening day of testing with a time of 1min 57.555sec.

"I was feeling quite good. We were focused on many things to try and make a good lap time and I think I did a good job," he said.

The 25-year-old Yamaha rider was fastest for most parts of Wednesday's session and claimed the fastest time on his 50th lap.

Six-time Spanish MotoGP world champion Marc Marquez came in second fastest with a time of 1:57.606 on his new Ducati machine, while his brother Alex Marquez was third after clocking 1:57.738. (AFP)