The attack took place in Camden at 11am, and the cyclist was forced to defend himself with his bike after being approached by the aggressor.
Despite the man attempting to attack the commuter, many passers by continued to walk past without intervening.
SUSSEX MAN SHOOTS DAUGHTER, 8, BEFORE TURNING GUN ON HIMSELF
An anonymous eye-witness said: "I was sat on the top deck of the bus when the incident unfolded.
"I first noticed the driver was beeping somebody furiously, but couldn't see anything extraordinary so assumed it was just traffic flow - then the man appeared in the street brandishing a knife. He was very aggressive and clearly had the capacity to kill.
"The attack was very one-sided, with the victim having to defend himself by using a bicycle as a makeshift shield, which no doubt saved his life.
"People were stunned. Onlookers and fellow passengers were screaming for help - but it all happened so quickly, there was no time to think clearly. Even in the safety if the bus it was terrifying.
"Eventually, another man jumped in and the attacker fled - leaving everybody stunned."
London’s Metropolitan Police later confirmed that two people had been arrested following the incident, one for possession of an offensive weapon and the second for police obstruction.