National Lottery players are being urged to check and double-check their tickets for the chance to claim the life-changing prize.
The National Lottery says the £124,270 ticket is most likely tucked away in a wallet, purse or coat pocket.
The se
arch is now on to find the owner of the winning ticket, which was bought in the Havant area.
The ticket was bought on Saturday, December 5.
The ticket matched five numbers and the bonus ball in the Lotto draw on the same day.
Patrick Lisoire, spokesman for the National Lottery, said: 'We're desperate to find this mystery ticket-holder and unite them with their winnings - this amazing prize could really make a huge difference to somebody's life.
'We're urging everyone to check their old tickets again or look anywhere a missing ticket could be hiding.'
The winning ticket in Havant, if claimed, would come as another cash bonanza in the area. As reported in The News, a Gosport cabbie has been partying for days after telling friends he has won the lottery jackpot.
Tony Pepall has told family and friends he was the only person to match all six numbers in the draw on December 16, which would have netted him £2,900,560.
Neighbours at his home in Russell Street, Gosport, have told about the celebrations being thrown at Mr Pepall's house.
Lottery operators Camelot have, however, refused to confirm the winner's identity.
Mr Lisoire said the Havant winner had until 5.30pm on Thursday, June 3 to claim the prize.
If no-one comes forward with the winning ticket before the deadline, the prize money, plus all the interest it has generated, will go to good causes.
Mr Lisoire added: 'Try checking in the pockets of clothing, in wallets, bags and down the back of the sofa - someone out there could literally be sitting on a fortune!'
The winning Lotto numbers on December 5 were 8, 20, 36, 43, 45, 49 and the bonus ball was 12.
The National Lottery claims number is 0845 910 0000.
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