ADELAIDE ruckman Reilly O'Brien has re-signed with the Crows in a move that could affect whether they pursue Collingwood star Brodie Grundy.

O'Brien, 23, has been rewarded for his breakthrough season by signing a two-year contract extension until 2021.

Having only played two senior games before this year, O'Brien has become the Crows' first-choice ruckman since round three when he replaced an injured Sam Jacobs.

He has retained his spot ahead of veteran Jacobs, averaging 14.9 disposals and 34.7 hitouts per game.

 "The Crows have shown enormous faith in me, so it's fantastic to be able to sign a new deal and commit to the Club," O'Brien said.

"It's been awesome to get the opportunity to play more senior footy this year and being able to contribute to the team."

The Crows could still make a play for South Australian Grundy who is a free agent at the end of 2020, but O'Brien has shown he's capable of holding his own at senior level.

The Crows will now turn their attention to re-signing key defender Alex Keath and midfielders Hugh Greenwood and Cam Ellis-Yolmen, while Jake Kelly, Riley Knight and David Mackay are also off-contract.

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