The 48-year-old was walking along Poplar Avenue in Bearwood when he was approached by a knife-wielding man.
The victim, who was stabbed in the arm, ran to a bus that was parked up while the offender fled the scene on Tuesday.
Emergency services rushed to the scene on nearby Sandon Road – where the victim was – at around 1.35pm.
West Midlands Ambulance Service said the man was treated for his injuries before being taken to hospital for further treatment.
An ambulance and the West Midlands Care Team were both sent to the scene, a spokesman for the ambulance service said.
CCTV is being reviewed by police as investigations continue anyone with information should contact them on their website via 101.
Crimestoppers can be called anonymously on 0800 555 111. Quote crime reference number 20BW/256210P/20.