The victim was found unconscious and with a serious head injury in Essex Street, just off the A38 Bristol Street, at around 1.30am on Friday.
He was rushed to hospital and was in a critical condition.A man, aged 26 and from Erdington, was later arrested in nearby Digbeth High Street on suspicion of wounding.
West Midlands Police said he was known to the victim.
Essex Street is close to city centre attractions including the Hippodrome theatre and the Arcadian Centre, a complex of bars and clubs.