Flutter Entertainment said today that Matt King, the chief executive officer of its FanDuel business, will be leaving the company and the betting group warned his exit would delay FanDuel's potential US listing.
Flutter's shares fell more than 3% in Dublin trading after the news.
The owner of Paddy Power, Betfair and PokerStars also said it was keeping the FanDuel floatation under review and was looking for a successor to King.
"With FanDuel well positioned for the next chapter of its growth and always an entrepreneur at heart, now is the time for me to take on new opportunities as the next step in my career," King said in a statement.
Flutter said King had been the top boss at FanDuel for four years and that he had overseen the growth of the online sports betting and gaming business after a 2018 lift on a ban on sports betting made the United States the next big growth market.
Last month, Flutter reported that its first-quarter US sales more than doubled almost exclusively through FanDuel, in which the Irish company increased its stake to 95% through a $4.2 billion deal in December.
King's decision to leave FanDuel was "clearly a disappointment," analysts at Davy Research said in a note.
However, they added that the role is likely to attract "high calibre" candidates because of the opportunity to lead the "best positioned" US sports betting operator.
Peter Jackson, CEO of Flutter Entertainment, said that FanDuel had achieved so much in the three years since the Professional and Amateur Sports Protection Act (PASPA) in the US was repealed.
"We are starting the process of looking for a new CEO for FanDuel and we remain focused on maintaining our leadership position in the US market," he added.