Silver King, 51, collapsed suddenly in the ring on Saturday at the Roundhouse, a performing arts and concert venue in Camden, London.
Britain's Press Association reported that Gonzalez's opponent, Juventud Guerrera (Spanish for "Youth Warrior") knocked him to the canvas twice.
"A champion luchador in his native Mexico, Silver King, real name Cesar Cuauhtemoc Gonzalez Barron, entertained audiences across the globe, and was a standout in WCW's Cruiserweight division in the late '90s".
The Round said there had been an "incident" at the show but the venue was unable to comment further.
A World Championship Wrestling star has died in front of hundreds of fans after collapsing during a match in London on Saturday night.
In a video that has since surfaced, King can be seen knocked down, squirming on the ground - a common choreograph among wrestlers during matches. Such a frightful situation, my heart goes out to all involved as well as to his loved ones.
"Sad news today, he wrote on Twitter, Silver King died in London". He & Tejano were an awesome team. He became famous for playing the villain Ramses in the film "Nacho Libre". Like so numerous great Luchadores that helped Americans appreciate Lucha Libre and make Nitro the success it was, he will be missed. They declared that Barrón died at the scene.
WWE ( World Wrestling Entertainment) said in a statement it was "saddened" to learn of his death. WWE Hall of Famer Sean Waltman said, "It was an honour to have been friends & shared the ring with the great Silver King".