A motorcyclist, who was trapped under a van following a crash near Stroud, is said to be in a stable condition at Bristol's Frenchay Hospital.
The collision happened just after noon on Friday on the A419 at Chalford.
Great Western Ambulance Service said the victim suffered potentially life-threatening injuries.
Gloucestershire Police want to speak to another biker, seen overtaking a lorry at the time of the crash, who might have seen what happened.
He was described as riding a "powerful bike".