The 58-year-old man, who has not yet been named, was involved in a collision with silver/grey coloured Skoda Fabia in Halton on Monday, December 12.
A police spokesman said: "The cyclist was taken to Leeds General Infirmary in a serious condition and died this morning (Thursday).
"Officers are continuing to appeal for witnesses - and in particular anyone who saw either the car or the cyclist - immediately before the collision or the collision itself."
The incident happened shortly after 7.30am on the A6120 Ring Road near to the junction with Whitkirk Lane, close to the Colton roundabout.
Anyone who witnessed the incident is asked to contact the Major Collision and Enquiry Team on 101, quoting log number 249 of December 12.