Forsyth, who can play as a left-back or as a left-sided midfielder, has been ruled out for the rest of the season with a cruciate knee ligament injury.
The 26-year-old suffered the injury during Derby’s Championship game against Queens Park Rangers at the iPro Stadium.
The Scotland international was taken off in the 21st minute, as the Rams went on to win the game 1-0.
Barker, who left Derby at the end of the 2014-15 campaign, has wished his former teammate Forsyth a speedy recovery on Twitter.
Gutted to hear the extent of Fozzy's injury. Been brilliant for @dcfcofficial since he signed. Good luck to him on his road to recovery!— Shaun Barker (@barks5) November 5, 2015
Derby are fifth in the Championship table at the moment with 30 points from 15 matches, just a point behind leaders Hull City.
Paul Clement’s side will take on Nottingham Forest away from home at the City Ground in the league on Friday evening.