German cyclist Matthias Kessler remains hospitalized in critical condition after sustaining head injuries in a crash this week.

The Son Dureta Hospital said Saturday that the 30-year-old Kessler has undergone surgery to treat his injuries.

Kessler has been in the hospital's trauma unit since the accident in nearby Agaida on Wednesday. He sustained severe head injuries after falling off his bike during training.

Kessler, a former Team Telekom rider, tested positive for testosterone while with Astana in 2007 and was suspended for two years.