The incident involving a motorcycle and a BMW car on the A5104, happened just before 13:00 BST on Monday, 29 August.
North Wales Police want to speak to the driver of a dark coloured vehicle which was overtaken by an orange motorbike prior to the collision.
The injured motorcyclist was flown to the Royal Stoke University Hospital in Stoke-on-Trent.
A motorcyclist has suffered "life-changing" injuries following a collision at Bryneglwys, Denbighshire.