Jones Jr. -- a multiple time world champ across 4 weight classes -- says he would NEVER quit inside the ring.
"When I go in the ring. Carry me out. I don't wanna go out on my feet if I lost. Carry me out. I rather give it all, or get it all taken away from me."
Still, RJJ says all ain't lost for Khan -- a fighter he likes and respects -- as long as he gets real about what happened.
"Amir, I love you as a fighter. I respect you since you were an amateur fighter. You went up 2 weight classes, took on Canelo. You did a lot of beautiful things to show that you have courage," Jones Jr. says.
"This time you were in a no-win situation, and you refused to continue," Jones tells us ... "You stopped at a time we know you could've given more. You didn't give it to us, the fans, your all."
"You have to apologize. We respect that. Be a man. Be honest for what you did, and move forward."