The jackpot of £7,440,150 is yet to be claimed from a Lotto ticket bought in Wolverhampton, West Midlands, on 18 June.
Players are being urged to check their tickets to see if they have the winning numbers.
The Lotto jackpot winner matched all six main numbers in the draw, which were 11, 14, 36, 39, 42, 59 and the bonus ball was 21.
Andy Carter, senior winners’ advisor at The National Lottery, said: “We’re desperate to find Wolverhampton’s mystery Lotto jackpot ticket-holder and unite them with their winnings.
“We’re urging everyone to try checking in the pockets of clothing, in wallets, bags, down the back of the sofa and anywhere a missing ticket could be hiding.”
The winner has until15 December 2022 to claim their prize.
On Saturday, another lucky person won a £20m Lotto jackpot.
The winner came forward on Monday and is currently undergoing a validation process. Once they have been through validation, they will decide whether or not to go public with the news of their winnings.
Mr Carter said: “We’re delighted that this special £20m ‘Must Be Won’ Lotto jackpot has been claimed. Our focus is now on supporting the ticket-holder through the process and helping them start to enjoy their truly life-changing win.”
The biggest National Lottery win of all time was £195m at the EuroMillions jackpot in July.
Only 15 UK players have won a jackpot of more than £100m, including the previous record-holders, Joe and Jess Thwaite from Gloucester, who won £184m in May.