The 28-year-old was rushed to hospital following the collision, which involved a motorbike and a car, in Halifax yesterday (June 15).
It happened at the mini roundabout of Furness Drive, Bank Edge Road and Bank Edge Gardens at around 5.55pm.
A West Yorkshire Police spokesperson said: "The vehicles involved in the collision were a silver Vauxhall Zafira and a motorbike.
"The Zafira was travelling from Bank Edge Gardens towards Furness Drive and the motorbike was travelling towards West Bank when a collision occurred as they entered the roundabout.
"The 28-year-old driver of the motorcycle suffered serious injuries and was taken to hospital for treatment.
"Anyone who witnessed the collision or has any information is asked to contact the police via 101 quoting crime reference number 13180290943."