ADELAIDE ruckman Sam Jacobs will play his first game as second fiddle to young draftee Reilly O'Brien on Thursday night against Geelong.

Jacobs jarred the medial ligament in his knee in January but has been back training fully for a number of weeks.

O'Brien impressed in his first senior opportunity in the club's opening NAB Challenge clash against North Melbourne in Port Lincoln on March 1, winning 14 hit-outs and eight disposals.

Crows coach Phil Walsh said the 19-year-old would lead the club's ruck department against the Cats in an attempt to ease Jacobs back into action.

If O'Brien continued to perform, the coach said he'd debut against North Melbourne in round one.

"I was really happy with how Reilly performed last week, (he) did the majority of the ruck work and he'll probably do the same again and we'll manage Sam back in his first game," Walsh said.

"If Reilly goes well again I'll play him again against Port (in the club’s final NAB Challenge game).

“(If) he puts pressure on (Josh) Jenkins, it puts pressure on how we use Jacobs – all those things.

"I've spoken to the players, if you play well you stay in the team and that's how it works."

Forward Tom Lynch will also face the Cats after being knocked out against the Kangaroos.

Lynch ducked into Jack Ziebell's hip and immediately fell to the ground in a worryingly similar incident to when he broke his neck against the Brisbane Lions in round 20 last year. 

He was given the all clear by club doctors on Monday and will play on Thursday night at Simonds Stadium. 

The Crows dominated the first three quarters against the Kangaroos in Port Lincoln but almost lost the match when they faded badly.

Walsh was far from pleased with the final term effort but said he had no issue with the fitness of his players.

"In my time in footy, I've been in it a long time – some might argue too long – but this group's worked as hard as any group in a pre-season," he said. 

"I'm very happy, we've got excellent fitness staff here, it was a good alignment with my philosophy on conditioning and theirs and we've worked really well as a team.

"So no, I'm happy in that regard."

Club champion midfielder Scott Thompson won't play on Thursday after suffering a hamstring setback.

Thompson endured a persistent back-related hamstring problem last year, which restricted him to 19 games and probably cost him a third Malcolm Blight Medal as the club's best and fairest.