Police were called at approximately 10:25hrs on Monday, 19 April to Bow Roundabout, E3 close to the A12 following reports of a collision involving a van and cyclist.
Officers and the London Ambulance Service attended the scene.
The cyclist, a 30-year-old a man, was taken to an east London hospital where he remains in a critical condition. His family has been informed.
The driver of the vehicle stopped at the scene and enquiries to establish the circumstances of the collision are ongoing.
Detectives from the Roads and Transport Policing Command are investigating.
Anyone with information or who may have captured the collision on dash cam or other media devices is asked to contact the witness appeal line on 020 8597 4874, quoting Cad 2162/19Apr.