Police in Hillingdon and paramedics rushed to West End Road at around 6.45pm on Friday (October 13) following reports of a stabbing.
Officers first shared a tweet about the incident while en route to the scene: "En route to a male reportedly stabbed in the abdomen in Ruislip," it read.
The man was found near the junction with Mason Avenue suffering a serious stab wound and was taken to hospital.
A spokesman for the Met on Saturday (October 14) confirmed the man remained in a critical condition.
Earlier, the force said:"Officers attended along with London's Air Ambulance.
"The victim, a man believed to be in his 20s, was taken to a central London hospital."
A pictured shared on Twitter by a passer-by showed emergency services in attendance.
The spokesman added no arrests have so far been made and enquiries are ongoing.
Anyone with information is asked to call the Metropolitan Police on 101 or call Crimestoppers charity anonymously on 0800 555 111.
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