Adelaide defender Brodie Smith handed his tough-as-teak teammate Luke Brown a nice birthday present to take into the Preliminary Final when he injured his knee in the Qualifying Final.

Smith gift-wrapped Brown, who turns 25 on Friday, the kick-in duties for the rest of the finals.

Brown is a good player to take on the responsibility, having taken 57 kick-ins this season, way ahead of the third Crow in line, Jake Lever, who has done the job 18 times in 2017.

But Brown is not Smith, who had taken 77 kick-ins this season, the most of any Crow and the 15th most in the AFL.

Smith is very good at taking a quick kick-in after a behind, which increase's Adelaide's chances of outnumbering the opposition across half-back and breaking through the press.

The Crows have been the best in the AFL at getting the ball into their forward half from a kick-in, with 26 per cent of kick-ins sending the ball across the centreline and into the open spaces Eddie Betts and Josh Jenkins roam.

With the territory battle so crucial to the result, the loss of Smith's skills getting the ball back into play in should not be underrated, particularly given Geelong has improved its press in recent times.

It makes Crows' ruckman Sam Jacobs such a critical player, as he shapes as a natural target for the Crows when kicking out, and Smith's absence also forces players other than Brown to take the pressure kick from time to time, making them more vulnerable than they otherwise would have been.

Birthday boy Luke Brown will be the Crows' go-to for kick-ins on Friday night. Picture: AFL Photos

That's not the only hole that Smith leaves however.

His rebound from half-back is a key reason why the Crows can be so aggressive and direct when they attack.

Smith loves to sit off the back of stoppages and explode off the line when his midfield teammates win possession, receiving handballs and lateral kicks to race the ball up the ground.

He averages a club best 24.2 metres gained per disposal and has formed a brilliant rebounding combination with All Australian Rory Laird.  

Against Geelong in Round 11, Sam Menegola quelled Smith’s influence but he took Steve Motlop and Jordan Murdoch apart when matched up on them in Round 18.

The best candidate to fill Smith's big shoes is versatile midfielder David Mackay who averages a handy 20.9 metres gained per disposal, can run and has a deep kick.

David Mackay - another Crow who must step up against the Cats. Picture: AFL Photos

Mackay's defensive game has improved and he has done jobs on creative wingers such as the Dockers' Brad Hill, Greater Western Sydney's Tom Scully and West Coast's Andrew Gaff in 2017.

Given Rory Sloane will replace Smith after missing the qualifying final, the reshuffle should be minimal with Paul Seedsman playing on a wing and Richard Douglas pushing forward as he did against Geelong in round 18, particularly if Mitch McGovern is missing.

Mackay is experienced enough to understand the set-ups at key stoppages, but he will still have to co-ordinate his movements with a back six that has been stable most of the season.

Smith's absence leaves a hole that Brown and Mackay must fill.