A 34-year-old motorcyclist from Notton suffered life threatening injuries after he was thrown from his bike.
Police believe the man, who was riding a blue Honda motorcycle along Royston Road in Cudworth, Barnsley, was involved in a collision.
It happened at around 6.45pm on Friday, March 7.
Police want to speak anyone who witnessed the collision.
They are also keen to trace the driver of a light-coloured car that seen driving along Royston Road towards Cudworth at the time of the incident.
Anyone with information should contact South Yorkshire Police on 101 or call Crimestoppers anonymously on 0800 555111.