German track cyclist Kristina Vogel has been seriously injured after crashing in training in the eastern city of Cottbus.
German news agency DPA reports that the Olympic champion suffered a severe spinal injury after crashing onto a concrete track following a high-speed collision with another cyclist on Tuesday.
"We're very worried about Kristina. It looks very bad," German coach Detlef Uibel told DPA.
Vogel, an 11-time world champion, was taken to the local hospital before being flown to Berlin.
Vogel's manager, Joerg Werner, said she was "seriously injured" and that she would need to undergo surgery through the night. He did not give any further details.
The German Cycling Federation (BDR) said Vogel had been training with Pauline Grabosch, and that she accelerated when Grabosch left the track - only to collide with another unidentified cyclist who entered suddenly.
Vogel was training for the German Grand Prix, which was due to take place in Cottbus on Friday and Saturday.
The Lausitzer Rundschau newspaper reported that it could be cancelled.
The 27-year-old Vogel also had a serious accident in May 2009, when she was knocked off her bike by a vehicle.
She suffered severe injuries and was placed in an artificial coma for two days.
But she returned three years later to win the team sprint for Germany with Miriam Welte at the London Olympics.
Vogel became the first German to win gold in the sprint in Rio four years later despite a broken saddle.
Vogel edged out Australian Stephanie Morton at the individual sprint ICU track championships in March to claim an eleventh world title, going level with fellow Australian Anna Meares on the all-time women's list.