"I have decided to retire young. Thanks for the cheese. Catch ya's later," read Conor McGregor's tweet
Retweeted 140,000 times, the post sent shockwaves through the MMA community, with the Irish fighter's coach John Kavanagh then tweeting: "Well was fun while it lasted."
Fans were divided on whether the retirement was genuine, or whether the colorful fighter was merely trying to drum up media interest ahead of a scheduled July rematch with Nate Diaz, who handed the Dubliner the first defeat of his UFC career last month.
A subsequent statement from UFC president Dana White announcing that McGregor had been pulled from the July 9 main event against Diaz only served to add further intrigue to the Irish fighter's retirement tweet.
White said the fighter had been withdrawn after he had told UFC officials he would not participate in promotional activities for the UFC 200 event in Las Vegas, including a commercial shoot and press conferences.
The UFC president said his organization was working on arranging a substitute main event to replace the Diaz and McGregor bout.
Diaz, the 31-year-old American fighter who defeated McGregor by forcing a second-round tap-out in Las Vegas last month, also weighed in on the discussion of his rival's future.
"I guess my work here is done I'm retiring too," he tweeted.
According to McGregor's social media accounts, the fighter, known as "The Notorious," is currently training in Iceland.
His retirement claim comes a week after the death of MMA fighter Joao Carvalho, from injuries he sustained during a fight in Dublin.
McGregor, who was ringside at the fight, paid tribute to the Portuguese fighter on Facebook, calling him "a champion, who pursued his dream doing what he loved."
"It is such a rare occurrence that I don't know how to take this," he wrote.