Officers are appealing for witnesses and dashcam footage following a collision in Christleton.
The incident took place on Whitchurch Road at around 3.40pm on Thursday 10 December and involved a cyclist and a lorry.
The cyclist, a 14-year-old boy, was taken to hospital by air ambulance.
His condition is described as serious.
The driver of the lorry stopped at the scene and is assisting police with their enquiries.
Officers want to speak to any drivers who believe that they may have captured any footage to come forward.
Anyone with information or dashcam footage that may help the investigation is asked to call Cheshire Constabulary on 101 quoting IML 870470 or report it via https://www.cheshire.police.uk/ro/report