Dani Pedrosa could miss the next three races of the World Championship after the Spaniard broke his collarbone in practice for the Japanese MotoGP on Friday.
Pedrosa, who won last year’s race, suffered a spectacular highside on a 90 degree corner.
He is expected to return for the season finale at Valencia in November although he could return to action sooner.
Former 250cc World Champion Hiroshi Aoyama, will be the Spaniards replacement in Japan.
Yamaha’s three-time and reigning world champion Jorge Lorenzo set the fastest pace during the dramatic session.
The 29-year old Spaniard is hunting a fourth win this season and lead Ducati’s Andrea Dovizioso, who has had a roller coaster campaign retiring from five races so far in 2016.
With Pedrosa out for an undetermined amount of races, Maverick Viñales will have his eyes set on moving ahead of his compatriot into fourth in the overall standings.
The Suzuki rider was third fastest in the practice session.
Championship leader and Marc Marquez – the 2013 and 2014 world champion – was fourth quickest around the Motegi circuit.
Britain’s Cal Crutchlow was fifth on his Honda ahead of Spanish Suzuki rider Aleix Espargaro.
Italian multiple world champion Valentino Rossi, who is second in the standings 52 points behind Marquez, was seventh on the day.