The incident occurred around 10:30 p.m. Thursday on the 400 block of Domino Lane.
Police say 53-year-old Joseph Fullam was found lying int he middle of the street by a passerby, who then alerted police.
Fullam was rushed to Albert Einstein Medical Center where he remains in critical condition.
According to his neighbors in Roxborough, Fullam is essentially homeless, living mostly in a truck owned by a resident for whom he does odd jobs.
Investigators have no information on the striking vehicle.
Anyone with information is asked to contact police.