McGregor, 27, who’s still scheduled who was scheduled to fight Nate Diaz at UFC 200 on July 9, holds a 19-3 career record.
MORE: McGregor’s most notorious moments | McGregor: A UFC fighter for non-UFC fans
(UPDATE: The UFC announced Tuesday evening it had pulled McGregor from UFC 200 after McGregor “informed UFC officials that he would not participate in any promotional activities, including a commercial shoot and press conferences.)
(UPDATE 2: UFC president Dana White told ESPN later Tuesday that McGregor’s refusal to participate forced his hand. “Obviously we still have a good relationship with Conor,” White said. “I respect Conor as a fighter and I like him as a person. But you can’t decide not to show up to these things. You have to do it.” )
MUEHLHAUSEN: Retirement would be a gut kick to UFC
McGregor’s tweet was was posted a week after MMA fighter Joao Carvalho, 28, died from injuries suffered during a fight — a match in McGregor’s home country of Ireland that he attended.
MORE: Top UFC villains ever
McGregor’s coach, John Kavanagh, appeared to comment on/confirm the retirement with a tweet later Tuesday.