The 374-litre cask, originally filled on May 5 1988, has been held in bond at the Macallan Distillery in Moray for almost 34 years.
It was bought on a whim by an expat who then forgot about it for more than three decades until they were reminded by Macallan that it was still maturing in the warehouse.
Bids for the rare cask have already reached 170,000 dollars (£130,000) since the auction went live at 7pm on Friday and are expected to soar before the sale on the Whisky Hammer site ends on Sunday.
It is expected to break the record set in 2021 by Bonhams for the sale of a 30-year-old re-racked Sherry hogshead from Macallan, which fetched 574,000 dollars (£439,000).
Daniel Milne, co-founder and managing director of Whisky Hammer, said: “Casks of this age and size are extremely rare, especially from The Macallan.
“This is, without doubt, one of the most exciting casks we’ve seen come to auction in recent years and we expect it to set a new world record by the time the auction closes on Sunday.”
If bottled today, the cask would yield 534 70cl bottles.
The Whisky Hammer April auction, which includes more than 2,000 lots, is live until 7pm on Sunday.
Whisky Hammer is a family-run auction service founded by brothers Daniel and Craig Milne.