The 28-year-old man was riding his bike on the A944, about two miles east of Alford in Aberdeenshire, when his bike was struck by a silver Renault Clio.
The incident happened near the Mill of Bandley junction at 04:30 on Christmas Eve.
Police said the cyclist was taken to Aberdeen Royal Infirmary, where he is still receiving treatment.
Sgt Rob Warnock, from the Road Policing Unit, said: "Inquiries into the circumstances of the incident are at an early stage and I am appealing to anyone who witnessed the incident or came across it or saw the silver Renault Clio or the male cyclist prior to the incident to contact Police Scotland on 101.''
A cyclist is being treated for serious injuries after being hit by a car in the early hours of the morning.