Police are appealing for witnesses after the man was found injured in The Dale in Hathersage on February 27.
Officers were called to the scene shortly before 5.15pm on Saturday evening, following a report that a man had been found on the ground with a head injury.
He was treated by paramedics at the scene who described his injuries as life changing.
The cyclist was riding a burgundy road bike, which had a badly damaged wheel and police are investigating the possibility that he may have been involved in a collision.
Anyone who has information about how the man became injured is asked to contact PC Joseph Pickering quoting reference number 21*115805.
You can also anonymously contact Crimestoppers on 0800 555 111 or at www.crimestoppers-uk.org.