The serious car crash that sent 5-star hooper Alijah Arenas to the hospital with serious injuries was likely caused by excess speed, law enforcement sources tell TMZ Sports.

The Los Angeles Police Department was on the scene of the 5 AM crash, which occurred along a two-lane residential roadway in the Winnetka neighborhood of the San Fernando Valley, in a 40 MPH zone.

18-year-old Alijah was alone in the Cybertruck — owned by his father, ex-NBA star Gilbert Arenas — at the time of the accident … which was a single-vehicle wreck.

Our law enforcement sources say they believe excessive speed is the likely cause of the crash. Arenas is believed to have lost control of the electric truck before running into a fire hydrant and wrapping the truck around a big tree.

Thankfully, despite the accident happening before the sun even rose, residents living in the area heard the commotion from the crash, with multiple neighbors rushing outside to assist Arenas, who was inside the burning vehicle.

The fast-acting good Samaritans were able to free Alijah, who was then rushed to the hospital for treatment for smoke inhalation and other ailments, including bumps and bruises sustained during the wreck.

Good news, though … a rep for the Arenas family told us the top USC recruit, who many project will be a top 5 NBA draft pick next year, is already on the road to recovery!