The pedestrian, a man aged in his 70s, was taken to hospital after a crash in Merley shortly before 10.30am on Friday, December 19.
His family has been informed.
The crash involved a silver Volkswagen Polo and a pedestrian in Sopwith Crescent, at the junction with Oakley Straight.
Road closures were put in place as emergency services dealt with the incident and were lifted at around 1.30pm.
Police Constable Calum Maton, of the Roads Policing Team, said: “We are investigating the full circumstances surrounding this collision and I am keen to hear from anyone who witnessed what happened or who may have captured relevant dashcam footage.
“I would also like to thank members of the public for their patience and understanding during the road closures.”
Anyone with information can contact Dorset Police online, via email at scit@dorset.pnn.police.uk or by calling 101, quoting occurrence number 55250186067.
Alternatively, independent charity Crimestoppers can be contacted anonymously online using its website or by calling Freephone 0800 555 111.