Paul Gallen said he would never box again in a social media video posted Saturday morning. "Father Time is undefeated and that's it for me," he said.
The 45-year-old had been knocked out in the first round of Friday night's heavyweight bout against Nelson Asofa-Solomona, a 30-year-old former Melbourne Storm enforcer.
Asofa-Solomona had a 30kg weight advantage and stopped playing NRL last year. Questions followed about whether the referee should have ended the fight sooner or disqualified Asofa-Solomona for continuing to punch Gallen against the ropes.
Gallen stayed down for several minutes before getting up, looking groggy and sore as he spoke with his son Kody.
Former Cronulla teammate Michel Ennis said on the Main Event broadcast: "I was scared mate, to be honest, at the back end."
Commentator Dan Ginnane said he was relieved the knockout would end Gallen's boxing career. "I always had the feeling he needs something like this, a devastating knockout, to finally put him out of his misery," Ginnane said.
Before the bout, Gallen told AAP his wife "wasn't happy" about his return. He said providing for his family was his motivation: "I provide for my family. I'm going to give my family a life I never had and that's my sole motivation."
In his Saturday video, Gallen said: "Everything is fine, no issues." He added: "I'm fine, fit and healthy and life goes on."