Olympic champion cyclist Kristina Vogel is stable after undergoing surgery for several hours overnight following a training accident which injured the German's spine.
"The operation went well. Kristina will continue to receive intensive medical care," a statement from the German Cyclists' Federation said on Wednesday.
The German collided with a Dutch junior rider at a track in the eastern German city of Cottbus on Tuesday and was transferred to hospital in Berlin.
Her manager Joerg Werner said the prognosis was unclear.
"At the moment, it is not really possible to say where this journey is going," he told DPA.
Jeffrey Kimmels, spokesman for the Dutch Cycling Federation, said the young rider she collided with at high speed was "OK. He has no serious injuries."
Vogel edged out Australian Stephanie Morton at the individual sprint ICU track championships to claim an eleventh world title in March, going level with fellow Australian Anna Meares on the all-time women's list.
Vogel, 27, won Olympic gold in the team sprint at the London Velodrome in 2012 and individual sprint gold in Rio de Janeiro four years later.
Miriam Welte, part of the 2012 team, told DPA that she was "shocked and in disbelief" over the accident and the apparent seriousness of Vogel's injuries.
She was training ahead of the German Sprint Grand Prix, which will still take place as planned on Friday and Saturday on the cycle track in Cottbus.
"We consulted with the national coach and decided to go ahead with the event," Axel Viertler, head of race organisers RSC Cottbus, told DPA.
