Adelaide coach Neil Craig has challenged young ruckman Jonathan Griffin to demonstrate the aggression and persistence required of an AFL ruckman if he wishes to figure in September.

In the absence of recuperating tall Brad Moran (torn posterior cruciate ligament), the Crows have given second ruck duties to James Sellar, a player who Craig does not see as a long-term ruck option.

That has left the talented but placid Griffin in the SANFL, where he is yet to convince Craig his natural ability has been sufficiently steeled by a fierce attitude.

Griffin's future is clouded with several clubs reported to have expressed an interest in the WA-raised ruckman.

Craig said he had seen no evidence that Griffin wanted to do anything other than fight for his place in the Crows' best 22.

But in describing why he had persisted with Sellar instead of Griffin, Craig argued that the former's competitiveness had won the day.

"James has done an admirable job in the last seven weeks," Craig said on Friday.

"He has held up in a lot of situations better than I expected, particularly at the centre bounce. I like his aggression in there.

"He's becoming more active around the ground, in terms of his mobility and knowing where to go and not just becoming a ruckman for stoppages.

"Jon Griffin will bring a different edge, at 200cm plus to start with so he could in theory give you more at the centre bounce, (but) in the end we've just pulled back to performance.

"I like what Jon did last week in the second half for Centrals and it's that sort of performance that will enable him to put pressure on Ivan and James."

The imperative of one-on-one contests between ruckmen dictates that Craig wants to see a certain level of fight in his talls.

"I'm sorry but if you want to be a ruckman you're put into an environment where it's quite clearly you and me for this contested ball," Craig said.

"Sometimes I have to actually run at you, by law. That doesn't happen to little back pocket players.

"And so that's a really important trait.

"We know that Jon can do it, and it's not the only part of his game (he needs to work on) but that often kick-starts a lot of the areas.

"What I saw in the second half last week will be good enough, but he needs to do it not just for a half of footy in the SANFL."

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