Boxer Julio Cesar Chavez Jr. Arrested For Felony Possession Of Assault Rifle

Julio Cesar Chavez Jr. was arrested for illegal possession of an assault rifle this weekend in L.A. ... after cops were called to the scene by a concerned fan who believed the boxer may be a danger to himself or others.

TMZ Sports has learned the 37-year-old former champ, son of the legendary Mexican pugilist Julio Cesar Chavez Sr., was taken into custody by LAPD around 1:30 PM ... after Jr. permitted responding officers to enter his home, where they located the illegal rifle.

Law enforcement sources tell us the weapon was an untraceable "ghost gun."

Chavez Jr. was ultimately transported to the Valley Jail in Van Nuys ... where the 6'1", 170 lb. fighter was booked.

It's not the first time people around Julio have feared for his safety. In fact, Chavez Sr. recently opened up about fears his son could lose his life if he continues down the same path.

Speaking of his God-like figure of a dad, although Julio didn't come close to the astronomical success his dad achieved in the squared circle, Jr. finished his boxing career with a 53-6-1 record ... fighting the likes of Daniel Jacobs and Canelo Alvarez.