The 11-year-old was injured after an incident just before 1pm on Sunday
The driver failed to stop at the scene after hitting the boy while he was attempting to cross Highlands at the junction with Hereford Way.
Police say the driver continued down Sussex Drive.
The victim and was taken to hospital by ambulance, where he underwent surgery and remains in a stable condition.
Investigating officer PC Jon Simpkins, of the Joint Operations Roads Policing Unit, said: “I am appealing for any witnesses to this collision, whereby a young boy has sustained serious injuries, to please come forward.
“The boy had just got off the B9 Stagecoach bus before the incident so someone on the bus may have seen what happened.
“Also, if you were driving in the area around the time of the collision and have dash-cam, I’d also ask that you check any recordings in case it has captured something that could assist our investigation.”
No arrests have been made.
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