Police responded just after 4:15 a.m. to the area of Butterfield Road south of Golf Road for the reported crash.
Police said a dark-colored sedan traveling south on Butterfield hit a 60-year-old Grayslake man, who was also riding south, and did not stop, continuing south on Butterfield.
The bicyclist was taken to Advocate Condell Medical Center in Libertyville with life threatening injuries, police said. He remained in critical condition later Thursday.
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Butterfield was closed in the area for several hours.
The suspect and vehicle have been located using a license plate reader, police said.
It was not immediately clear if the suspect was in custody.
Anyone with information is asked to call Vernon Hills police at 847-362-4449.