The winning ticket for Saturday's Lotto jackpot of £5,268,052 was sold in Dixie's newsagent, Swords, Co Dublin. It is not yet known if the winning ticket - a £6 Quickpick - was bought by an individual or a syndicate.
Dixie's proprietor, Mr Leonard Flynn, said somebody local was likely to have won as most of his business was from the area. However, he said the Lotto had not contacted him.
"It hasn't been confirmed. It could be an April fool joke. The first I heard of it was when a newspaper rang to inquire about the ticket," he said.
If the ticket belonged to an individual he or she would be the second highest winner ever, according to a Lotto spokeswoman.
The highest individual win to date was £6.2 million, while the highest jackpot won was £7.2 million. Mr Flynn will receive £7,500, which is taxable, the Lotto spokeswoman said.
The winning numbers were 33, 1, 28, 38, 13, 23 and the bonus number was 14.