The UFC has “postponed until further notice” Monday’s news conference featuring Conor McGregor and Michael Chandler in Dublin.
McGregor, 35, is scheduled to fight American Chandler at UFC 303 on 29 June in Las Vegas.
The Irishman was due to face the media alongside 38-year-old Chandler at the 3Arena.
BBC Sport has asked the UFC for an explanation.
“When we have further information on a new date and time, we will share it immediately,” a statement from the UFC said.
McGregor had been due to conduct several interviews on Sunday but they were also cancelled at short notice.
Chandler and UFC president Dana White were both scheduled to travel from the US to attend the news conference.
The UFC announced the fight on 24 May and tickets sold out in fewer than 10 minutes.
McGregor, who is based in Dublin and trains at SBG Gym under his head coach John Kavanagh, has not fought on home soil since 2014.
The former featherweight and lightweight champion has fought just four times in the UFC since becoming a two-weight champion in 2016.
