With just a week left until the claim deadline, the winner, from East Dunbartonshire, is being urged by Camelot to come forward to collect their prize.
The player and two other individuals from Fife each scooped £1m from EuroMillions Millionaire Raffle draws in the summer of last year.
The National Lottery is urging players to search for old tickets and check the numbers.
For every EuroMillions line played, UK players automatically receive a EuroMillions Millionaire Raffle selection printed on their ticket.
Two of the winning tickets are from the draw on July 26 when 100 lucky players were guaranteed winners of £1m each.
The other winning ticket is from July 23.
The East Dunbartonshire winner has until 11pm next Wednesday to claim their prize. The winning ticket was CBT475280
A National Lottery spokesperson said: "There are three lucky winners in Scotland not knowing they are millionaires."