The woman who accused McGregor of assault said it happened in December at the Beacon Hotel in Dublin, according to the newspaper.
Police in Dublin have not confirmed that McGregor is a suspect. When asked about an "unnamed sportsman," the Gardai, the Irish police service, said a man was arrested, but released on Jan. 17, the Post reported.
McGregor has not commented on the allegations.
Original report: In a move that has surprised some, mixed martial arts fighter Conor "The Notorious" McGregor has announced his retirement from the sport via Twitter.
>> Read more trending news
"Hey guys quick announcement," McGregor tweeted late Monday. "I've decided to retire from the sport formally known as 'Mixed Martial Art' today. I wish all my old colleagues well going forward in competition. I now join my former partners on this venture, already in retirement. Proper Pina Coladas on me fellas!"
The 30-year-old fighter, originally from Dublin, Ireland, is a two division UFC world champion and two division Cage Warriors World Champion. He's ranked No. 2 lightweight champion and No. 9 pound for pound champion in the UFC, according to Fox Sports.
Yahoo Sports reported the announcement came as a surprise, and that McGregor may "just be trying to get an upper hand in a negotiation."
McGregor appeared Monday on The Tonight Show with Jimmy Fallon and made no mention of retiring, MMA Fighting reported. He talked of fighting this summer.
“We’re in talks for July,” McGregor told Fallon. “So we’ll see what happens. A lot of politics going on. The fight game is a mad game. But again, like I said, and to my fans, I am in shape and I am ready.”
Some fans on Twitter seemed unconvinced of the news.
"Last time he said this he fought twice in the next 6 months," tweeted @BishopSportsNet.
UFC hasn’t yet commented on McGregor’s announcement.