Cooper said he had rejected a contract with the Australian Rugby Union after being offered an incentive-based deal usually awarded to fringe squad members.
The 24-year-old will instead make his boxing debut on the undercard when close friend Sonny Bill Williams faces South African Francois Botha in Brisbane on February 8.
"It (boxing) is been a big interest for me after following Sonny and Choc (Anthony Mundine) and when I caught a live fight the first time and saw how they trained," Cooper said in Brisbane.
Cooper, recuperating from a knee injury, said he will continue to train with the Queensland Reds, with whom he is currently contracted till the end of the year.
"Boxing has been used as a bit of a release, a bit of a way to work on my cardio," Cooper said. "As it stands now, I'm still contracted until the end of December.
"I don't really have an option to continue with rugby at the moment, so for now I'm just focusing on getting my body right.
"I'm still training with the Reds, I'm still contracted with them. I'm just putting my full focus on getting my body right for the upcoming boxing fight."
The outspoken New Zealand-born player was recently fined A$40,000 (£26,000) for describing the Wallabies camp as a "toxic environment".
The fine completed a miserable 12 months for Cooper, which started when he limped out of the World Cup with a damaged knee after being labelled "public enemy number one" in the land of his birth.
Cooper has since been linked with a move to either the Japanese or French leagues or Australian rugby league, where former All Black centre Williams - New Zealand's heavyweight boxing - will play next year.
Though he remained non-committal on his future plans, Cooper insisted his passion for rugby remained intact.
"Rugby is the game I love. I was brought up playing rugby union and rugby league," he said. "For me the desire will never go and it's something that I hold close to my heart.
"My desire for rugby will never fade but it's kind of out of my hands at the moment."
Cooper is listed as 92 kilos on his Queensland profile, just over boxing's cruiserweight limit and putting him in the same heavyweight category as Williams.
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