The versatile 27-year-old has played 81 games – including 17 last year – after switching from basketball in 2008. He began his career as a forward, but has since found his niche as a mobile defender.

The club announced in 2014 that Henderson had “signed a two-year contract extension which will keep him at the Crows until at least the end of 2017”.

However, the AFL today unveiled its free agent list for 2016, with Henderson surprisingly declared an “unrestricted free agent” – meaning he can walk to the club of his choice without the Crows having the option to match any rival offer.

Compensation – to be determined by the AFL – is unlikely to be significant, with Henderson dogged by injuries throughout his career since being rookie drafted in 2008 and elevated via pick 82 in the 2010 national draft. But he is nonetheless an important component of a developing backline, especially with the recent shock retirement of Matthew Jaensch.

Veteran midfielder Scott Thompson and former captain Nathan van Berlo are also classified as unrestricted free agents, however both will be over 30 at season’s end and neither are considered likely to see out their careers elsewhere.

A Crows spokesman told InDaily: “As a club, we don’t comment on contract negotiations in a public forum.”

However, it’s understood the club is confident Henderson will remain in Adelaide colours beyond this season. The confusion appears to relate to the structure of his contract, which is believed to have clauses that trigger an extension beyond this season.

Nonetheless, it adds weight to recent arguments for player contracts to be more transparent.

Neither Adelaide nor crosstown rival Port have any restricted free agents this season, after speculation about the future of star onballer Patrick Dangerfield – now at Geelong – dogged the Crows throughout last year.

Power veteran Paul Stewart, who played much of last season in the SANFL, will be an unrestricted free agent at year’s end.

And there could be more headaches for strife-struck Essendon, with a glut of its players – including reigning club champion Cale Hooker – classified as unrestricted free agents.

The Bombers are vulnerable to a poaching raid, with Fremantle reportedly courting the versatile 27-year-old backman, one of 12 current Essendon players banned for this season in the fallout from the club’s 2012 supplements program. Courtenay Dempsey, Heath Hocking, David Myers, Tayte Pears and Brent Stanton are also listed as unrestricted free agents.

Seven players – including Brisbane’s Daniel Rich, Collingwood’s Steele Sidebottom and Melbourne’s Jack Watts – were classed as restricted free agents, meaning their clubs can match any rival offers and have the right of first refusal over the player’s services.

Introduced at the end of the 2012 season, the controversial free agency system has seen some big names swap clubs, including marquee forward Lance Franklin to Sydney, Dangerfield to the Cats and goal sneak Eddie Betts to Adelaide.

2016 FREE AGENTS

Restricted

Daniel Rich (Brisbane Lions); Nathan Brown, Steele Sidebottom (Collingwood);Jack Grimes, Jack Watts (Melbourne); Ty Vickery (Richmond); Sean Dempster, (St Kilda).

Unrestricted

Ricky Henderson, Scott Thompson, Nathan Van Berlo (Adelaide Crows); Daniel Merrett (Brisbane Lions); Dennis Armfield, Kade Simpson (Carlton); Jarryd Blair, Brent Macaffer, Dane Swan, Alan Toovey (Collingwood); Courtenay Dempsey, Heath Hocking, Cale Hooker, David Myers, Tayte Pears, Brent Stanton (Essendon); Zac Clarke, Matt de Boer, Chris Mayne, Matthew Pavlich, Clancee Pearce, Aaron Sandilands (Fremantle); Jimmy Bartel, Corey Enright, Tom Lonergan (Geelong Cats); Luke Hodge, Sam Mitchell, Brendan Whitecross (Hawthorn); Neville Jetta, Jake Spencer (Melbourne); Michael Firrito, Brent Harvey, Drew Petrie, Lindsay Thomas, Daniel Wells (North Melbourne); Paul Stewart (Port Adelaide); Sam Fisher, Leigh Montagna, Nick Riewoldt (St Kilda); Kieren Jack, Ted Richards (Sydney Swans); Mitchell Brown, Sam Butler, Patrick McGinnity, Will Schofield (West Coast); Matthew Boyd, Will Minson, Dale Morris, Robert Murphy (Western Bulldogs).