A man is fighting for life in hospital after falling off his bicycle in inner-Brisbane on Friday.

The 67-year-old local man fell on Oateson Skyline Drive in the eastern Brisbane suburb of Seven Hills about 6am.

Passers-by rendered first aid until paramedics arrived and later took the man to the Princess Alexandra Hospital in a critical condition.

Police believe the cyclist may have suffered a medical episode moments before the fall, but have appealed for any witnesses or anyone with vision from the area to come forward.