IT'S hard to imagine that a 24-year-old with just 20 career games under his belt could be his club's most important player, but that's the scenario facing Adelaide ruckman Reilly O'Brien heading into next season.

The 202cm O'Brien is the clear-cut first-choice big man at the Crows after veteran Sam Jacobs joined Greater Western Sydney in the off-season.

Untried rookie Kieran Strachan is the club's only other specialist ruckman, while Port Adelaide recruit Billy Frampton can also be used in the middle.

BEST 22? Who's in, who's unlucky for your club's R1 team

Strachan – the tallest player on the Crows' list at 204cm – played the majority of his first season at the club as a key forward in the SANFL before going into the ruck in the last month.

The 24-year-old was picked up in the rookie draft last year on the back of a handful of VFL games and strong form for South Bendigo.

02:38

Crows land 'the Jeremy McGovern' of the draft

Cal Twomey and Riley Beveridge analyse Adelaide's draft

Frampton, 200cm, is considered a key forward who can pinch-hit in the ruck.

His two games for the Power this year were as a forward, kicking three goals in two games.

In his only game at senior level as a starting ruck, Frampton had 15 hitouts and seven disposals in the round 23 clash with Essendon in 2018.

New Adelaide recruit Billy Frampton has played most of his senior career as a forward. Picture: AFL Photos

At a pinch, the Crows could throw 198cm tall forward Elliott Himmelberg into the ruck, while draftees Fischer McAsey (197cm) and Josh Worrell (195cm) have the height – but not yet the strength – to also be part-time options.

But without a doubt, O'Brien is head and shoulders above the rest.

Originally a rookie draft selection in 2015, O'Brien bided his time behind Jacobs – apart from a taste of senior football in round 20-21 of the 2016 season – before finally having an extended run in the side this year.

He got his chance in round three when Jacobs was sidelined with a shoulder injury, going on to average 33.3 hitouts and 15.3 disposals in 18 games in a stunning breakout season.

Crows ruckman Reilly O'Brien does battle with then-Blue Andrew Phillips. Picture: AFL Photos

Like the majority of ruckmen, O'Brien has had his own injury issues, missing a chunk of the 2017 season with a back injury and 2018 with a shoulder reconstruction.

The Crows decided against picking up a ruckman in the national or rookie draft, but still have a list spot open which they could fill in the supplemental selection period.

The Crows have more accomplished players – such as captain Rory Sloane, the Crouch brothers and key defender Daniel Talia – but O'Brien is the one they can least afford to be without in 2020.