ADELAIDE has secured another key plank of its future with reigning club champion Reilly O'Brien penning a four-year contract extension.

The news comes on the back of a breakout 2020 season in which he earned his first Malcolm Blight Medal as the Crows' best and fairest winner.

The 25-year-old averaged 27 hitouts and nearly two contested marks per game last season as he lifted his game to a new level.

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"This allows me to invest in the group and really focus on others as well," O'Brien said after penning his new deal, which ties him to the club until 2025.

"I'm really comfortable in Adelaide and excited with where the club is heading, I want to be part of something special and help build that from the ground up and this is a great opportunity to do that."

O'Brien famously made himself a target last year when he accidentally tweeted out game notes ahead of Adelaide's clash with West Coast.

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"Run off him hard, he is lazy and unfit," O'Brien wrote on Twitter. "Will have a field day getting ball and marking everything.

"Get to front and have grunt around the ground, and get ball on deck, beat him in this area." 

Adelaide's social media team had a field day on Thursday as they announced O'Brien's new deal.

O'Brien joined the Crows as a rookie in 2014 before making his AFL debut in 2016.

Adelaide list boss Justin Reid said O'Brien was crucial in the club's rebuild.

"Reilly is a hard-working, highly-talented ruckman who we value enormously and that was evident in him winning the club's best and fairest and the Members' MVP Award last season," Reid said.

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"He demonstrates all the values we want our players to display, is professional with the way he approaches his football and his influence on game day is significant."

O'Brien joins the likes of Brodie Smith, Harry Schoenberg, Rory Laird, Andrew McPherson and Josh Worrell in recommitting to the club.