Conor McGregor admitted he was "heartbroken" Sunday after a shock UFC knockout by underdog Dustin Poirier left the superstar's future in the cage uncertain.
"It's hard to take," Irishman McGregor told a post-fight news conference.
"(It's) the highest highs and the lowest lows in this game. I don't know where I'm at, at the minute, to be honest," said the biggest drawcard in mixed martial arts.
The 32-year-old McGregor had been an overwhelming favourite to register a winning return after a year away from the octagon.
But Poirier (27-6), who lost in 109 seconds to McGregor in their first fight in 2014, used a lower leg kicking strategy to negate his opponent's stand-up style.
The American then launched a sustained barrage of blows to the head culminating in a straight right dropping McGregor to the floor moments before the fight was stopped at 2min 32sec of the second round.
"I have no excuse. It was a phenomenal performance from Dustin. It's a bitter pill to swallow," said McGregor, who hobbled onto to stage with help of a crutch and revealed his calf had blown up "like an American football."
The unexpected defeat left many MMA fans wondering what will be next for McGregor, who will face questions about his future in the sport.