Dean Leacock has joined Leyton Orient on a deal until the end of the season after having his Derby contract cancelled by mutual consent.
Leacock was set to be out of contract at Pride Park in the summer anyway and has now had his deal cut short.
The 27-year-old centre-half is the sixth player to leave the Championship club in recent weeks.
Russell Anderson, Chris Riggott, Stephen Bywater and Stephen Pearson all had their contracts cancelled, while David Martin joined Southend in an undisclosed deal.
Leacock joined Derby from Fulham in August 2006 and helped the Rams to win promotion to the Premier League in his first season at the club.
The last of his 126 appearances came in a defeat at Reading in the final game of last season.