Mills featured 136 times between 1998 and 2006 before taking a one-year hiatus at Crawley and returning to make another 17 appearances in 2007.
Stints with Tamworth and Stevenage followed before joining the Stags in 2009, where he played 46 games.
He was loaned out to Forest Green Rovers for two months earlier this season but made just one start.
Source: BBC Sport
Source: BBC Sport