At around 8.30pm on Saturday, 4 September, officers on patrol came across a disturbance in Station Approach, Barking.
During the disturbance, the base of a traffic cone was thrown, hitting the victim and causing him to fall to the ground.
Officers administered first aid and the man, aged in his 30s, was taken to hospital suffering a head injury. His condition is critical.
Detectives from East Area CID are investigating. Enquiries are ongoing to identify those involved, including the male who threw the object.
Anyone with information or any witnesses are asked to call 101, ref 6738/04sep. To remain anonymous, please contact Crimestoppers.
There has been no arrest. Enquiries continue.