Hermann Hreidarsson could quit Charlton for free after more than four years at the club, BBC Sport understands.
Hreidarsson has played 149 games for the Addicks
The Icelandic international defender's present deal runs until 2009.
But the 32-year-old has a clause in his contract which allows him to leave the Valley for nothing following Charlton's relegation from the Premiership.
It is the fourth time Hreidarsson has been relegated from the top flight after also going down with Crystal Palace, Wimbledon and Ipswich.
Hreidarsson, who has more than 50 international caps, went down with the Eagles in 1998, Wimbledon two years later and Town in 2002.
And this season he was unable to help the Addicks climb clear of danger after a slow start to the campaign.
He was one of four players to make 30 or more league appearances, but his own goal at Blackburn in late April proved a costly mistake in a 4-1 defeat which left Alan Pardew's team with too much to do in their final two games.
A 2-0 defeat at home to Tottenham in their penultimate game sealed Charlton's fate after seven years in the Premiership.