A £5m lottery ticket remains unclaimed a week after the draw, operator Camelot says.
The ticket contains the winning numbers in the 28 September Lotto draw - 3, 15, 20, 48, 57 and 58 - and it was bought in a shop rather than online.
Andy Carter, senior winners' adviser at The National Lottery, said that finding the ticket "could be life-changing".
Players should check their paper ticket either in store or by scanning it on the National Lottery app.
He said: "It's been a busy month or so for me and my team with Lotto making an amazing 14 millionaires since the beginning of September and we hope this lucky Lotto streak continues.
"Each and every winner has a chance to change their life and the lives of the people around them, whether that be with homes, holidays or supporting causes close to them."
If the prize is not claimed within two weeks of the draw, Camelot will reveal the general area in which the ticket was bought, as a way of encouraging people to check.
Any National Lottery winner has 180 days from the day of the draw to claim their prize if they have the winning ticket.
Once a ticket-holder has contacted Camelot and their claim to the jackpot has been validated and paid, they can decide whether to go public or remain anonymous.