Nottingham Forest and Matt Mills have reached an agreement to cancel the centre-back's contract early, potentially paving the way for a free transfer to Barnsley.
The 31-year-old leaves the City Ground having made 72 appearances for the club since arriving from Bolton Wanderers in 2015.
Mills has started 11 times in the Championship this term, most recently in the 1-0 home defeat against Aston Villa on January 13, but he is now officially a free agent.
Barnsley have been linked with the English defender over the past few days and may now consider bringing him on board as any fee has been waived.
Forest moved to bring in Tobias Figueiredo on loan from Sporting Lisbon earlier this week.