FIVE years ago, the $250,000 Tim Serisier won on Who Wants To Be A Millionaire allowed him an indulgence he'd only ever dreamed about. Now he feels it's time someone else took on the burden, and so Australia's most iconic item of sporting memorabilia is about to go under the hammer.

The auctioneer Charles Leski admits the vendor's timing could be better, but has still placed an estimated price of $600,000 to $750,000 on the baggy green cap worn by Don Bradman on the 1948 "Invincibles" Ashes tour.

A Bradman bat sold recently for a world record $145,000.

"I defy anybody to tell me anything in Australian sport that is more important or has a higher status," Mr Leski said yesterday, ahead of the December 15 auction. "This is the single most valuable item we've ever auctioned - sporting, Australiana, across the board."

The cap is accompanied by a memo signed by Bradman in 1996 that both verifies its authenticity and hints at its colourful life, declaring that "on his twelfth birthday I gave Richard Robins one of my Aust. XI caps".

Richard Robins's father, Walter, played 19 Tests for England and was described by Bradman as his "best pal in the cricket world" - despite bowling the great man with a googly to which Bradman offered no shot in the 1930 Trent Bridge Test.

Serisier, a 47-year-old retired banker from Coffs Harbour, bought it prior to auction in 2003, amid a campaign to return it to Australia. He paid $425,000, and was hit with a $42,500 GST bill because it was a collectible item.

Peter Hanlon