Medal favourite Barnes was stunned by Spain’s Samuel Carmona on a split decision, ending his dream of finishing on the podium at a third consecutive Olympic Games.
But within minutes of the defeat, Barnes was the target of online critics who hit out at his performance and questioned his preparations.
However Conlan, who fights next Sunday in the bantamweights, launched staunch defeat of his team-mate and friend last night.
He tweeted: “The fact some of you idiots on here giving Paddy Barnes stick is a f**king disgraceful, what he’s done for the country is unbelieveable.
“2x medalist 3x time Olympian & use (sic) keyboard warriors at home doing nothing with your lives but criticising him without a clue about boxing!
“Paddy Barnes is a Legend of Irish sport and always will be! Done a lot more for Ireland than most ever will!”
Barnes’s devastating defeat put him out of the Olympic tournament but he will remain a valuable member of the team within the athletes’ village.
“He’s the life and soul of the camp,” said John Conlan, one of the team coaches and father of Michael.
“The boxers are professionals, they’ll get on with it.
“They’ll sit down and they’ll joke a little bit about him being the first out.
“But Paddy’ll do his job as the leader here, supporting everybody.”
The next Irish into the ring today will need plenty of Barnes’ support.
David Oliver Joyce won his first bout on Sunday but he now has to face Albert Selimov, a very challenging customer.
Selimov won the lightweight silver at last year’s world championship and gold at the European Games.
He has a point to prove in Rio as his failure to qualify for Russia’s 2012 Olympic team saw him to switch to Azerbaijan.
“This is the Olympic Games, there’s no easy draws,” said Conlan.
But Joyce dismissed any concerns. “I’ll focus on him tomorrow. I’m in the arena where I am meant to be, and that is where I box my best,” said the St Michaels Club, Athy, man.
“I box at a high pace, and that’s what fuels me and gets me through my fights.
“I performed well in my first fight but now I know I have to step it up.”