Conor McGregor lost a significant bet against former UFC champion Francis Ngannou. The two fighters placed a wager on Ngannou's return fight in the Professional Fighters League (PFL), with McGregor backing Renan Ferreira to knock out Ngannou. However, Ngannou won via first-round knockout, leaving McGregor $500,000 poorer.

Source: https://www.forbes.com/sites/brianmazique/2024/10/20/conor-mcgregor-loses-big-in-failed-bet-against-former-ufc-champion/