A woman has since been arrested on suspicion of attempted murder and driving while unfit through drink or drugs.
The man, aged in his 40s, was left with significant head injuries after being hit by a car in Reservoir Road, Erdington, at around 10pm on Friday.
The vehicle left the scene but has since been recovered and a 44-year-old woman has been arrested, West Midlands Police said.
The suspect, who is known to the man, remained in custody on Saturday morning as the man was in a critical condition in hospital.
Reservoir Road remained closed on Saturday while specialist police officers examined the scene.
Anyone with information is asked to contact police quoting log number 20/1792022/21.