125cc World Championship leader Marc Marquez, winner of the last five races, has been sent for medical checks after injuring his arm during a highside at the end of Friday practice at Brno in the Czech Republic.
Marquez - leading the championship by 26 points over Pol Espargaro - finished the session in third for Red Bull Ajo Derbi, behind the Aspar Aprilias of Nicolas Terol and Bradley Smith.
UPDATE: Marquez has been diagnosed with a dislocated shoulder.
Former world championship leader Terol made a remarkable return to action, after missing the previous Sachsenring round due to back injuries sustained in Catalunya, to lead the session by 0.507sec from his British team-mate.
After a slow start, Espargaro rose to fourth fastest for Tuenti Derbi, 0.812sec behind Terol.
Friday practice - Brno:
1. Terol (Aprilia) 2m 8.010s
2. Smith (Aprilia) +0.507s
3. Marquez (Derbi) +0.788s
4. Espargaro (Derbi) +0.812s
5. Rabat (Aprilia) +1.444s
6. Webb (Aprilia) +1.815s
7. Krummenacher (Aprilia) +1.848s
8. Cortese (Derbi) +1.912s
9. Vazquez (Derbi) +1.928s
10. Zarco (Aprilia) +1.974s