The forward/ruckman played 32 games in five seasons at the Crows, but managed just nine games in 2013 despite Kurt Tippett's departure to the Sydney Swans and Taylor Walker's season-ending knee injury in round five.
McKernan, who turned 23 on Sunday, is out of contract and AFL.com.au understands his desire to return home to family and friends was the driving factor in his decision.
An Adelaide spokesman told AFL.com.au Crows list manager David Noble met with McKernan on Thursday but said the main topics of conversation were the tall's lingering groin issues and future opportunities at the club. He was adamant no decision had been made on McKernan's future.
The 196cm big man is mobile and athletic and should appeal to clubs looking for key forwards, with the Western Bulldogs, St Kilda and Carlton possible suitors.
It is understood McKernan is yet to actively pursue opportunities outside the Crows, but now the home and away season is over he is free to return to Melbourne and speak with clubs.
McKernan is the younger brother of two-time North Melbourne premiership ruckman Corey McKernan.
The Crows selected him with pick No.28 in the 2008 NAB AFL Draft.
Twitter: @AFL_Nick.
