Police were called at 159pm on Thursday, 14 February to reports of an assault inside a residential property in Northolt Road, South Harrow.
Officer and the London Ambulance Service attended and found man aged in his 30s injured, including a stab wound.
The victim was taken hospital. His injuries are not life-threatening or life-changing.
The victim had pre-arranged a viewing of the property and to that end had let two males and a female into the address.
The victim was then assaulted by the males before all three made-off on foot.
Nothing was reported stolen.
Officers carried out a search of the area and a 29-year-old man was arrested on suspicion of robbery and possession of a Class B drug (cannabis).
He was taken to a north London police station and was subsequently bailed to return on a date in mid-March.