A 31-year-old man has been placed under arrest by NSW Police, two days after a stabbing in Sydney's inner west resulted in the death of a 32-year-old man.

On Monday, at around 7:40pm, emergency services were called to Marrickville Road in Marrickville following reports of a street fight.

When paramedics arrived, they discovered a 32-year-old man unconscious outside a fast food outlet. 

The 32-year-old man later died at the scene.

NSW Police confirmed the alleged victim and offender were known to each other.

CCTV footage showed the offender running down Silver Street in Marrickville after the attack.

According to NSW Police, at around 5:40pm on Wednesday, a 31-year-old man was arrested in the inner west suburb of Concord.

He is currently in custody and is assisting police with inquiries.

Investigators have appealed for anyone with information, dashcam or mobile phone footage to contact Marrickville Police Station or Crime Stoppers.