Brad Pitt has been “extremely concerned” for his estranged son Pax after the bike accident that nearly killed the 20-year-old, and he’s been getting a steady flow of information about his recovery … TMZ has learned.

Sources close to Brad tell TMZ … he was shocked and emotional after learning about the accident. TMZ broke the story … Pax was riding his e-bike without a helmet along an L.A. street on July 29, when he plowed into the back of a car idling at a red light.

Pax was unconscious … it was so bad eyewitnesses thought he had died. Pax suffered a serious head injury with brain bleed, as well as a hip injury. Paramedics rushed Pax to an ICU unit, and he stayed in the ICU for a week before being released. He’s now on the mend.

Brad and Pax are estranged … the result of a nearly 8-year, never-ending, bitter divorce from Angelina Jolie. Our Brad sources have previously claimed she has turned all their kids against Brad, some of whom have now dropped Pitt from their names.

Brad has no direct contact with Pax, but our sources say “concerned people around the family” have been giving him information about Pax’s injuries and his recovery … for which Brad is “grateful.”

We’re told Brad is “extremely concerned” about Pax’s well-being, and given Brad always wears a helmet when he rides a motorcycle, it’s alarming to him Pax almost never wears a helmet.

He’s concerned Pax has been in multiple accidents in recent months. We’re told Pax wrecked his car earlier this year and has been involved in at least one other e-bike crash.