Ben Spies' first Japanese MotoGP as a Factory Yamaha rider got off to a 'shocking' start when he was forced to curtail Friday practice due to severe food poisoning, picked up en route from the USA.

Treatment at the Clinica Mobile on Thursday evening helped the Assen winner find enough strength for 18 laps in morning practice, where he finished in eighth, 0.9sec from the front.

But exhaustion then set in, resulting in an early end to the afternoon session after just five laps.

"What a shocking start to the weekend, I don't think I've ever been as sick as I was on the journey over here, I was nearly not allowed on the plane," said Spies. "I'm slowly getting my strength back thanks to the great guys at Clinica but didn't have enough to ride properly in the second session.

"I started to get tunnel vision on the straight and just felt it was too dangerous to be out there. I'm working with Clinica today and tomorrow and am sure things will be a bit better for qualifying and the race. I'm really sorry for my team and all the Japanese fans who came to watch today."

Team director Massimo Meregalli is confident Spies will be in better shape for Saturday's track action.

"We are working together with Clinica Mobile and Ben's condition is getting better all the time," he said. "Yesterday he had some treatment and it helped him complete this morning's session. He thought he could also do the second but I think he used up all his energy in the first heat. We think tomorrow will be better and Sunday he will hopefully be ready for the race."

Team-mate and reigning world champion Jorge Lorenzo was fifth fastest during a Honda-dominated opening day.