That's former boxing superstar Ricky Hatton UNLEASHING on his former opponent Floyd Mayweather ... essentially saying the exhibition with Logan Paul was an INSULT to the sport he loves.

42-year-old Hatton -- The Ring magazine's 2005 Fighter of the Year -- HATED everything about Floyd vs. Logan and went off the two in a scathing IG post early Monday morning.

"My personal opinion that was s**t for boxing," Hatton said.

"What happened to the days where fighters would put there lives on the line to try be the best and at least fight the best."

"Now we have fighters calling out youtubers as that’s where the most money is these days due to the social media world we live in???"

"I can live with an exhibition like mike (Tyson)and Roy (Jones) did between two legends of our sport but the greatest fighter of all time who has only recently retired against somebody who’s only there cus of how many followers he has and not because of who he’s previously beat???"

"Money is important that’s why we went from the amateurs and turned pro. But these days money seems more important than the legacy."

Yeesh.

Hatton was 43-0 when he fought Floyd back in 2007 -- but Mayweather kicked his ass ... ultimately winning in a 10th round TKO.