The incident happened at about 5pm on Friday, April 15, when the boy was cycling along Heanor Road in Loscoe.
A black Renault Clio with four or five people in it drove past the boy and fired what is thought to be a BB gun at him. A pellet struck him on the cheek causing reddening.
Officers are appealing to a dog walker who was on the street at the time to come forward as he might have vital information.
Witnesses should ring the police on 0345 123 33 33 and ask for PC Louisa Briscoe.