Rival clubs have reportedly begun to express their interest in Lions key defender Darcy Gardiner.

The 26-year-old's soon-to-be free agency status has highlighted his predicament as one of few key position players on the trade market heading into next season.

Contract discussions between Gardiner and the Lions were reported to have begun long ago, but no deal has been reached as Gardiner approaches his 150th game, with the end of the home and away season looming.

"He’s a bit of a forgotten free agent, he’s one of only three restricted free agents that are left unsigned at this late stage of the year,” AFL reporter Callum Twomey told SEN.

"The others are Jordan De Goey and Lance Franklin.

"We’re obviously all taking about those guys but Darcy Gardiner is still a restricted free agent but is not yet signed beyond this year.

"Contract talks have gone pretty slowly, they started earlier in the year, but no deal has been reached yet.

"Rival clubs are watching that one with some interest given the lack of key position players on the free agency market.

"I still think the most likely result is that he stays at the Lions but he’s the best key back out there in the free agency group.

"Attention is on Darcy Gardiner there at the Lions."

As a restricted free agent, the Lions would be able to match any rival offers for the Lions tall.

BRISBANE, AUSTRALIA - JULY 20: Darcy Gardiner handballs during a Brisbane Lions AFL media opportunity at The Gabba on July 20, 2018 in Brisbane, Australia. (Photo by Chris Hyde/Getty Images)

Gardiner has been a key member of Brisbane's backline since arriving at the club via the 2013 NAB AFL Draft and is a contract priority for the Lions.

He has has played 147 games for the club since arriving at the club via Pick 22 in the 2013 draft.