Brisbane have confirmed key defender Marcus Adams will not play again this season due to ongoing concussion symptoms.

Adams suffered a delayed concussion after a heavy hit in the Lions' Round 21 win against Carlton, and has been suffering health concerns since.

Adams' absence will continue to be a big loss for the club, who have the second worst defensive record out of teams in the top eight.

They also come up against Richmond in an elimination final on Thursday night, who have scored the most points out of any other team this season.

“We’ve had a bit of instability in our back six to be honest,” Lion coacgh Chris Fagan told SEN Breakfast on Monday morning.

“Since the bye we’ve played about a dozen players through there, if not more.

“We haven’t been able to stabilise it this week because we’ve lost Noah Answerth due to suspension and Marcus Adams looks like he’s done for the year with his concussion.

“There’s still a bit of a disruption there but that’s what this season is all about, giving opportunities to players and a lot of those guys who will play in the backline this week have played a few games this year and we look forward to them making a strong contribution.”

The Lions confirmed the diagnosis on Monday afternoon, with Adams joined by youngster Kalin Lane on the sidelines for the remainder of the season.

Adams' continued absence will more than likely allow 22-year-old Jack Payne to hold his spot at full back, whilst suspensions to Noah Answerth and Cameron Rayner will bring headaches to the Lions' selection table.

BRISBANE, AUSTRALIA - AUGUST 17: Marcus Adams of the Lions runs the ball during the round 22 AFL match between the Brisbane Lions and the Geelong Cats at The Gabba on August 17, 2019 in Brisbane, Australia. (Photo by Chris Hyde/Getty Images)

It is likely that utility Callum Ah Chee returns in the place of Answerth for a like-for-like swap, however the Rayner replacement seems to be a lot more up in the air.

The Lions have also noted that midfielder Jarrod Berry should be available for selection this week after overcoming an ankle injury, with the onballer train on Tuesday.

Livewire small-forward Kai Lohmann could be recalled to the 22, after having 17 touches and a goal in the Lions' VFL loss to Southport on Saturday, while have reported first-year defender Darcy Wilmot could make his debut against the Tigers.

First-year player James Tunstill is also a name that could replace Rayner, after he collected a team-high 25 touches in the VFL.

Darcy Fort however may be the most likely name to come into the side if Chris Fagan decides he wants to bring back the McInerney/Fort ruck duo that we have seen on several occasions this season.

The ruckman had 38 hit-outs and 16 touches in the loss to Southport.

The Brisbane Lions face finals dark horse Richmond on Thursday night at the Gabba in an all-to-play for elimination final.