David Copland, who as ‘Old Gloryhunter’ buys and sells historic medals, is looking for help to identify the player who won the medal.
Inscribed with the initials WP or PW, the medal was awarded to a Calne Town FC player in 1906-07.
The club had won the only League Championship, the Wiltshire League Division 2 Championship in 1906-07, it has ever achieved in its 134-year history.
The front of the medal is engraved with the player's initials, while the reverse has the details, ‘Winners Wilts League Division 2 1906-07’.
Mr Copland, 65, who lives near Richmond, bought the medal for £60 and has listed it for sale at £275 or near offer.
He has included some research on the medal and has found a postcard photograph of the Calne Town FC team with a trophy dated Season 1905-06.
Mr Copland said: “For fans and historians of Calne Town FC the medal for sale represents the holy grail.
“There are only 11 players featured in the photograph and it is likely only 11 League Championship medals would have been awarded.
“Over the years most will have been lost or even scrapped as some research is needed to link the engraving on the medal to Calne Town FC.
“It is certainly possible this medal is the last known survivor making it a scarce item.
“I would like to be able to identify the player who won the medal, as it is certainly a collector’s piece.”
The medal is in sterling silver with an applied gold shield to the front. It weighs 10.6 grammes and is 28 millimetres wide and 33mm high.
It is hallmarked with Birmingham 1906 and the maker's mark: Horace George Croneen.
Calne Town FC was formed in 1886 and in 1894 was a founder member of the Wiltshire League.
Mr Copland added: “The club struggled during these early years but won the Second Division Championship in 1906-07, which was a significant achievement.
“They have had some notable successes in the Wiltshire Senior Cup over the years but the 1906-07 League Championship win remains their only ever Championship.
“They are currently members of the Western League Division One and play at Bremhill View.
To view the medal or to purchase, go to www.ebay.co.uk and search for Calne Town FC medal.