Officers are appealing for information following a collision in Higher Ince in Wigan.
Shortly after 9:45pm om Monday 1 April 2019, officers were called to reports of a collision between a blue Ford Transit van and a motorbike on Ince Green Lane.
Emergency services attended and the motorcyclist, a 19-year-old man, was taken to hospital where he remains in a critical condition.
A 53-year-old man was arrested at the scene on suspicion of drug driving.
Enquiries are ongoing.
Sergeant Darren Hancock, of GMP's Serious Collision Investigation Unit, said: "This collision has left a man in a critical condition in hospital and my thoughts are with him, his family and his friends at this time.
"Our enquiries are continuing, and I would urge anyone who witnessed what happened to get it touch with police as soon as you can.
"We are particularly keen to hear from anyone with dashcam footage who was in the area at the time."
Anyone with information should call police on 0161 856 4741 quoting incident number 2425 of 01/04/19, or the independent charity Crimestoppers, anonymously, on 0800 555 111.