A man in his 20s was taken to hospital in a critical condition after an aggravated burglary in Harefield.
Police attended an address in Milne Way, Harefield, at around 1.15am on Tuesday (July 21).
A Metropolitan Police spokesman said: "A man in his 20s was taken to a west London hospital suffering with head injuries where he still remains in a 'critical but stable' condition.
"A second man in his 30s was also taken to a west London hospital. He has since been discharged."
After the incident, a witness said: "There was over 20 officers on scene yesterday (July 22) in the fields and knocking on doors."
The incident is now being investigated by officers from Hillingdon CID.
No arrests have yet been made and enquiries continue.