Marcus Adams leaves the field during Brisbane's win over Carlton in round 21, 2022. Picture: AFL Photos

DEFENDER Marcus Adams has been all but ruled out of the entire 2023 season as he continues to experience symptoms of a concussion he suffered last August.

Adams suffered delayed concussion symptoms following Brisbane's match against Carlton in round 21 and missed the remainder of the season.

More than five months on, the 29-year-old is still experiencing symptoms and the club said on Monday he is "unlikely" to play this year.

Marcus Adams is assisted by trainers during Brisbane's round 21 match against Carlton at The Gabba on August 7, 2022. Picture: AFL Photos

Adams has been moved onto the club's inactive list as he continues his recovery, which has opened up a spot on the Lions' list for this year.

"Unfortunately, Marcus is dealing with a serious injury that will unlikely see him play in 2023," said Brisbane's GM of Football, Danny Daly.

"While he is making some progress in his recovery from concussion, he continues to experience symptoms and his health and wellbeing remains the top priority.

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"The club is fully supportive of Marcus and his recovery, and he will remain involved with our footy program."

Adams played 18 games last season and 17 in 2021, establishing himself as a key part of Brisbane's defence having moved from the Western Bulldogs at the end of 2018.

Drafted by the Bulldogs as a 22-year-old in 2015, he is out of contract at the end of this year having signed a two-year deal in 2021. He will turn 30 in June.

Speaking last August when Adams was ruled out for the rest of the season, Lions coach Chris Fagan had expressed concern for the defender's welfare, saying a return to playing was secondary to his health.

Marcus Adams lays injured on the ground during Brisbane's round 21 match against Carlton at The Gabba on August 7, 2022. Picture: AFL Photos

"I'm hopeful for Marcus' sake that he can make a full recovery, not from a football perspective, but just from a personal perspective," Fagan told Fox Footy.

"I was chatting to him tonight and his spirit seems quite good. It's one of those unknown things as to what will transpire over the next weeks or months with it, but hopefully he comes good quickly.

"He's in good hands and all the right things are being done as we speak.

"He's worried about it. He's optimistic that he'll come right, which is great, but he's also, on the other hand, fairly nervous about it and hoping that he will come right.

Brisbane's Marcus Adams marks the ball against the Giants in round 11, 2021. Picture: AFL Photos

"So it's a bit of an unknown time for him and a difficult time.

"We'll wrap our arms around him as a footy club and make sure he gets all the help and expertise that he needs to hopefully get over this and first and foremost make a good recovery."

Adams managed just 27 games across three injury-plagued seasons with the Bulldogs and played just once in 2020 due to a foot injury.

Brisbane will open its 2023 season against Port Adelaide on March 18.