A copy of the surveillance video was turned over to California Lottery officials, the manager said.
The claim will be investigated, lottery spokeswoman Cathy Johnston said.
Lottery officials say someone who believes he or she is a winner must complete a claim form. But if someone loses a ticket, they must provide evidence that they owned it, such as a photograph of the front and back of the ticket, the officials said.
The winning numbers were: 23, 36, 12, 31, 13, and the mega number of 10.
The US$26 million prize can be taken in annual installments or as a US$19.7 million cash option. If the prize isn't claimed, the US$19.7 million will go to California public schools.
The store that sold the ticket will receive a US$130,000 bonus.
It's uncommon for large jackpots to go unclaimed, officials said.
Four prizes of US$20 million or more haven't been claimed since 1997, including a US$63 million prize from 2015, lottery spokesman Jorge De La Cruz told the Los Angeles Times.