Stetina, who twice won Colorado's Coors Classic and is a member of the Bicycle Hall of Fame, was injured Saturday when a Jeep sport utility vehicle collided with a group of cyclists along Lefthand Canyon, the Denver Post reported.
All of the other cyclists in the group were able to avoid the vehicle, which was being driven by a an adult man, except for Stetina, who lost control while trying to maneuver around the vehicle and fell off his bike. Stetina was wearing a helmet.
"He swerved and braked so hard he went over the handlebars," said Cpl. Heather Cobler of the Colorado State Patrol.
Stetina was airlifted to a hospital in Boulder where he was in critical condition, the Boulder (Colo.) Daily Camera reported.
Wayne Stetina, the 57-year-old cyclist's brother, said doctors have not been able to give a prognosis, adding that they would know more after 72 hours.
The driver of the vehicle has not been charged, but police are still investigating the incident.