Newly crowned world champion Marc Marquez and polesitter Marco Bezzecchi crashed out at high speed after colliding in the opening lap as Spanish rookie Fermin Aldeguer won a chaotic Indonesia MotoGP on Sunday.
Spanish great Marquez "suffered an injury to his right collarbone" and will fly to Madrid for medical tests, his Ducati team tweeted, with fears he may have a fracture.
Ducati-Gresini rider Aldeguer pulled away and cruised to a maiden victory after Bezzecchi ran into the back of Marquez, sending both flying off their bikes, AFP reported.
Aldeguer finished more than six seconds ahead of KTM's Pedro Acosta in second and nearly eight seconds in front of teammate Alex Marquez in third.
"I don't believe it. I am super happy. To be a rookie, we are doing incredible work. We have to continue like this," said Aldeguer, 20, who secured his first MotoGP win.
Bezzecchi dominated in qualifying on Saturday with a lap record at the Mandalika track, but the Italian had a disastrous start on Sunday in humid conditions on Lombok island.
After slipping from pole to seventh behind Marquez, he tried to overtake the seven-time world champion but slammed into the back of him.
It sent the pair sliding into the gravel. Both walked away from the collision with Marquez -- who has a history of bad injuries -- clutching his right shoulder.
Ducati team manager Davide Tardozzi said there was evidence of a fracture on Marquez's right shoulder.
Marquez was crowned MotoGP champion last week at Japan's Motegi and had already set a single-season points record for a MotoGP rider of 545 before Sunday's race.
His points total was boosted by a sixth-place finish in the sprint because Luca Marini was hit with a post-race tyre pressure penalty.
Despite Aldeguer storming to victory there was a dramatic battle for the podium places between half a dozen riders.
Alex Rins' Yamaha began to falter and he fell out of podium contention as Alex Marquez rose to take third and increase his grip on second place in the overall standings behind his brother.
"I was a little bit better every lap. Congrats to my teammate, he had an amazing weekend. For us it is really important to be here on the podium," said Alex Marquez.
Brad Binder finished fourth, followed by Marini, Raul Fernandez and Fabio Quartararo.
Second-placed Acosta said he still wanted to improve but was content with a podium place after the frenetic battle with his rivals.
"We have to be happy all the time we are on the podium. We have many races where we have a good rhythm and a good potential, maybe not for the win but to be on the podium," he said.
Marc Marquez's Ducati team-mate Francesco Bagnaia, who started a lowly 16th on the grid, crashed out when he was last on the track in what was a dismal weekend for the two-time world champion.
Joan Mir and Enea Bastianini also crashed out.
Only 19 riders made it to the race's start line on Sunday, with Maverick Vinales withdrawing with an ongoing shoulder injury.
