Last month retired footballer Rio shocked sport by announcing he was aiming to step inside the ring and go toe-to-toe at the age of 38.
It comes after the former England defender hung up his boots in 2015 following a glittering career at Premier League clubs including Man Utd, Leeds and West Ham.
But undefeated Welsh boxing legend Calzaghe, 45, has blasted the attempt as a shameless bid for attention.
The former Strictly Come Dancing contestant also fears Rio’s total lack of experience could lead to him getting hurt.
“For me it is a joke”
The 2007 BBC Sports Personality of the Year winner told Daily Star Online: “I think it is a publicity stunt.
“It is not a game. Football is a game, cricket is a game. Boxing is a sport, you get hurt.
“For me it is a joke, I can’t see someone in another sport at the age of 38 coming to be a boxer.”
He continued: “I don’t agree with that sort of thing.”
Rio said he was hoping to join the pro boxing ranks because of his passion for the sport and is aiming to secure a British Boxing Board of Control licence.
The BBC and BT pundit is also good friends with British boxing golden boy Anthony Joshua, who even offered Rio the opportunity to spar with him.
In 2015 Rio was hit by the devastating death of his wife Rebecca Ellison from breast cancer at the age of 34, leaving behind the couple’s three children.
And the former Three Lions captain says boxing has become a helpful tool for him to cope with the tragic loss.
But the stinging comments from Calzaghe might force him to reconsider his hopes of exchanging blows for a living.
Calzaghe is widely regarded as one of Britain’s greatest ever fighters having fought an astonishing 46 fights without a single loss.
He hung up his gloves in 2009 after capping his stunning career with a dominant win over American veteran Roy Jones Jr at Madison Square Garden in New York.
Asked if he considered a comeback following the unanimous points decision, Calzaghe told us: “I knew before the Roy Jones fight that was my fight, I knew that my body was sore.”
10. Guillermo Rigondeaux (17-0-0, 11 KO’s)
He added: “For me it was being the best and beating the best. (But) I knew that was the end.
“There is a fine line between going on too long. I achieved what I wanted to achieve.”
It was previously revealed how “The Pride of Wales” lifted the lid on the time his dad almost got him beaten up by retired boxing supremo Mike Tyson.
Tensions threatened to boil over when a young Calzaghe asked “Iron Mike” for an autograph.
Daily Star Online has approached Rio for comment.