A 20-year-old man was arrested in Stanmore on suspicion of attempted murder on Tuesday, June 2, and has since been released under investigation.
Detectives from the North West Command Unit continue to investigate after a man was stabbed in Harrow.
Police were called just before 9pm on Monday, June 1, to Weald Lane.
Officers attended and found a man who reported he had been struck by a vehicle and then stabbed.
An 18-year-old man was taken to hospital; he has since been discharged.
The vehicle did not stop at the scene.
Enquiries continue to establish the full circumstances.
Any witnesses or anyone with any information is asked to call police on 101 or contact via Twitter @MetCC. Please quote CAD 7898/01JUN.
To give information anonymously contact Crimestoppers on 0800 555 111 or online at crimestoppers-uk.org