In a video statement, Butters said he felt it was time for him to move back to Victoria to spend more time with his family and friends after eight years in South Australia.
"Although I've loved my time in Adelaide and everything the city's given to me and the football club's given to me, I feel like I'm probably at a stage in my life where I'd like to get back around some family and friends and enjoy some more time with them and cherish their moments with them," he said.
He thanked his coaches, teammates and the broader club for taking a chance on "a skinny kid from Darley that had no shoulders".
"I'll always be a Port Adelaide person. I'll always value this club and what it's done for me," he said.
Butters has not yet nominated a club, with Geelong, the Western Bulldogs, Richmond and Collingwood all chasing his services across this year.
All have made club-record offers to Butters, with his move to a rival as hotly contested as any of the major trade moves this century, including Chris Judd's trade from West Coast to Carlton at the end of 2007.
As a restricted free agent, Port can match a bid on Butters and strike a trade. The Power have been adamant they would take that path with the superstar midfielder rather than accept a free agency compensation pick – which would be pick No.5 – under the free agency model.
https://www.afl.com.au/news/1594878/zak-butters-informs-port-adelaide-of-free-agency-call-as-victorian-clubs-circle