A crime scene is in place in Wealdstone after what police have described as a "serious assault".
An area of Wolseley Road has been taped off since around 1pm on Sunday (September 24).
The police cordon remained in place for 24 hours whilst an investigation was carried out.
Local police tweeted a picture of the crime scene, with two marked police vehicles, warning residents to stay clear of the area.
It read: "Wolseley Road Wealdstone closed due to police investigation - please avoid the area."
A Metropolitan Police spokesman confirmed on Monday September 25 a crime scene was still in place a day after the incident, describing it as a "serious assault".
We will be bringing you all the very latest updates on this story as it develops.
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Police have given an update following the incident on Sunday.
A man is in a “critical” condition after being found collapsed with a head injury - but how he sustained the injury remains a mystery.
Detectives are appealing for information after the man, aged 45, was found collapsed with a head injury on Wolseley Road in Wealdstone .
Officers and the London Ambulance Service attended the location at around 4.20am on Sunday (September 24).
A Met Police spokesman said:
“The 45-year-old man was taken to a central London hospital where he remains in a critical but stable condition.
“His next of kin have been informed.
“Enquiries into how the man came to sustain his injuries continue.”