Fellow German rider Danilo Hondo told Cyclingnews that the crash occurred when a cat ran into Kessler's bike while he was riding near Algaida, Mallorca.
Hondo heard the news from Andreas Klöden of Team Radioshack who was training with Kessler at the time of the crash. Hondo was told that Kessler, 30, is in critical condition with a severe head trauma.
Cyclingnews will publish new details as they arrive.
Kessler turned pro with Team Telekom in 2000. He joined Team Astana along with Klöden in 2007. That spring Kessler tested positive for testosterone and was suspended for two years. His suspension ended in July 2009.
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