The 30-year-old, who joined the Swans from Adelaide ahead of the 2008 campaign, played 117 of a possible 119 games over five seasons with the club, including last year's premiership.
But he revealed on Thursday he has struggled with hip problems ever since his first season as a Swan, to the point where he now struggled with "even the basic things of putting shoes and socks on in the morning".
As recently as Monday, coach John Longmire had hoped the important member of the backline would return to training this week and push for a recall, having missed the past three matches.
But the defender, who played a total of 222 games with the Crows and Swans, admitted he has battled the ailment for years before deciding on Tuesday enough was enough.
"It's both my hips," Mattner told reporters on Thursday.
"Six years ago I had surgery here on my left one and progressively my right one has been getting worse.
"I saw the surgeon at the end of last year with the idea of having surgery, but that didn't progress.
"In the off-season we did everything we could do try to get it right and that meant taking time off and having a restricted pre-season, but it just hasn't come good."
Despite his limited pre-season, Mattner was still back in his usual place in the back six for the Swans' season-opening game against Greater Western Sydney.
He would play the first seven games before finally succumbing to the pain.
"It sums up his mental strength," Longmire said.
"Not many of us knew the challenges, particularly over the last 12 months, that he was playing with.
"To play that consistent level and continue to train and contribute to the team was amazing."
Longmire pointed to two moments which he felt summed up the defender, who started his career with the Crows back in 2002.
In 2011, he gave Essendon's Brent Stanton a big head start, but still managed to chase him down and tackle him in the goal square to help preserve a five-point win.
Then in last year's Grand Final victory, he corralled Hawthorn's Grant Birchall on the boundary line and kept the ball in dispute, seconds before Nick Malceski's match-sealing goal.
Following the birth of his son Oscar in December last year, however, Mattner decided he needed to focus on life after football.
"The last year has been quite hard. The pain has been nearly every day," Mattner said.
"In the end (my long-term health) was probably the decision why I decided to give it away immediately.
"Even the basic things of putting shoes and socks on in the morning is quite challenging.
"So in terms of that, to live my life, I decided to make the decision."
James Dampney is a reporter for AFL.com.au. Follow him on Twitter: @AFL_JD