Mayweather Promotions’ unbeaten fighter Danny Gonzalez was shot and killed on Labor Day. He was 22.
The young fighter died Monday night, with TMZ reporting that he was shot in California about 9 p.m.
Two teenagers who were with Gonzalez had to be taken to hospital for treatment, and as yet no arrests have been made, nor has a motive been disclosed.
A police statement said: "Deputies arrived within minutes and located three male victims with gunshot wounds.
"One adult male succumbed to his injuries at the scene, and two minors were transported to a local hospital with non-life-threatening injuries."
Mauricio Sulaiman, WBC president, said: "We are very sad to report the tragic death of boxer and top prospect, Danny Gonzalez."
"We send our deepest condolences and prayers to the Gonzalez family at this hard time. May Danny rest in eternal peace."
Gonzalez’s promoter, Floyd Mayweather Jr., posted on social media: "R.I.P champ gone but never forgotten."
Gonzalez was signed by Maywether in 2016 and had three professional fights, the last coming in 2017 against Mario Ayala.