The incident took place after the Volkswagen almost hit the cyclist while trying to pull out into traffic.
Apparently enraged at the near miss, the cyclist jumps off his bike and gives chase as the panicked driver, 19, careers into another car, bringing him to a halt.
The man then pulls out a blade appearing to be more than 10 inches long typically used for survival or hunting purposes.
Brandishing the knife, he kicks the vehicle and slashes at the windows while the driver remains inside the vehicle.
The cyclist eventually manages to smash one of the windows, forcing the driver to flee the car.
The footage also appears to show two other boys run towards the scene, though there is no suggestion they knew either of the two.
No arrests have been made after the incident on Wednesday evening, Scotland Yard said.
The attack comes amid a knife crime epidemic in London that has so far claimed at least 37 lives this year.
A Met Police spokeswoman said: “Police were called on Wednesday, 30 May at around 17:00 hours to reports of males smashing a car window in London Road, Croydon.
“Officers attended and established that the driver of the car was approached by a male in possession of a knife who smashed his window.
“The victim, a 19-year-old man, in an attempt to escape, collided with another vehicle, exiting on foot. He was followed by the suspect.
“The victim later returned to his car after the suspect made off. No reported injuries. Enquiries continue.” SHARE THIS STORY USING ANY OF THE BUTTON BELOW ⬇ PLACE YOUR TEXT ADVERT BELOW ⬇⬇⬇