LOS ANGELES -- You don't have to dig too deep to realize Joseph Duffy gets under Conor McGregor's skin.

Duffy, who left mixed martial arts for three years, was signed to the UFC last year largely on his hype as the last man to defeat McGregor. On Oct. 24, in just his third UFC bout, Duffy will headline at Dublin's O2 Arena against Dustin Poirier in a lightweight bout, a main event which sold out in minutes.

But McGregor isn't too impressed.

"I think he's a journeyman," McGregor said at a recent media event in downtown Los Angeles. "I look at his career. He lost his Cage Warriors lightweight title that I lost, he submitted in the fourth round, he filled his s--- with excuses. He quit the sport. He moved countries, he changed teams."

McGregor, who lost to Duffy via first-round submission at Cage Warriors 39 in 2010, was just getting warmed up. He began questioning whether Duffy, a native of Donegal, Ireland of Welsh descent who lives in London, was truly Irish, or whether he's just taking a ride on McGregor's bandwagon.

"He was Welsh Joe, then he was London Joe, now he's Canadian Joe, then he sees my success and now all of a sudden he's Irish Joe," said McGregor. "I'd love to see him climb up and I will KO him stiff, just for the way this has all played out."

McGregor contrasted Duffy's career path to his own, noting Duffy left MMA after his only career loss, a fourth-round submission to Ivan Musardo at Cage Warriors 44, and pursued a boxing career.

"He loses the Cage Warriors lightweight belt and quits the sport, blames a broken hand, moves countries, changes teams, changes sports," McGregor said. "Then sees my success, my hard work. When I faced defeat, I put my head down and I grinded it and became a two-weight world champion in Cage Warriors and a UFC featherweight world champion. When he faced defeat he quit the sport and ran. Then he sees my success and my hard work and my drive and my dedication, and he decides to shave a shamrock in his head and calls himself Irish Joe and come back."

While there's no guarantee the two will ever cross paths in the cage, it's crystal clear McGregor welcomes the opportunity.

"I would definitely love to KO him stiff and put him in the ground or send him back to his other sport that he ran to after he lost," McGregor said.