ST KILDA veteran Sean Dempster has announced his retirement, saying he feared any further head injuries could impact his life after football.

Dempster, who had put his career on hold in the early rounds this season, confirmed the news to teammates on Thursday.

The 33-year-old said his most recent head knock against Port Adelaide in the JLT Community Series had made him think about his future in the game.

"I copped a little head knock and given my history over my career of receiving quite a few head knocks I've decided that it's a risk that's too great for me," Dempster told the club's website.

"Especially now that I've got a young family, it's more than just worrying about myself it's what it means to my wife and my young daughter.

"For the last couple of weeks the club has given me some time to myself and some time to go and get some independent testing done, which I'm still going through at the moment and is an ongoing assessment.

"The testing had nothing to do with my want to retire, I know it's the best thing to do for me and my family."

Dempster, a 2005 premiership player with Sydney before joining the Saints at the end of 2007, said his history meant the final call was easier than he expected.

The dependable backman was left out of the Saints' round one team against Melbourne, prompting questions about his fitness.   

After originally putting his absence down to form, the Saints confirmed Dempster was seeking medical advice to help decide if he wanted to continue his career.

"Whilst the medical consultation Sean is currently receiving coincides with him not being selected in the Saints senior team, there is no ill will between Sean and the club," football manager Jamie Cox said last week.

"He continues to receive our full support.

"Sean is a very private person and we wish to respect that while he seeks this advice."

Dempster was drafted to Sydney as a father-son selection with pick No.34 in the 2002 NAB AFL Draft, making his debut in round three, 2005, and playing in that year's premiership.

The last of the Swans' 2005 premiership players to retire, he played 54 games before joining the Saints and was a key player in the club's push to the 2009 and 2010 Grand Finals.

The versatile defender was named All Australian in 2012 and finished third in the Saints' best and fairest four times (2011, 2012, 2014, 2015).

Dempster is likely to be eligible for a payout, given his career has been cut short due to injury.

Brisbane Lion Justin Clarke and former Melbourne midfielder Sam Blease are two recent players who have retired early because of concern from head knocks.