Seven-time MotoGP world champion Valentino Rossi suffered a displaced compound fracture of his right tibia in free practice, after losing control of his Yamaha in one of the circuit's fast corners.
Dani Pedrosa dominated the MotoGP event aboard his Honda, reaching the finish line well clear of chasing championship leader Jorge Lorenzo in second.
Andrea Dovizioso took third, while ex-champion Casey Stoner took his Ducati to fourth on the final lap.
[2] The 125cc race saw the first victory of future multiple MotoGP world champion Marc Márquez.
Below are the standings for the top five riders and constructors after round four has concluded.