Johnson, who joined from Wolves in 2007, was a member of the Dons squad that won npower League Two and the Johnstone's Paint Trophy in the 2007/08 season.
A statement on the official club website read: "Everyone at MK Dons would like to thank JJ for his service to the club during his time in Milton Keynes and wish him every success in the future."
Source: PA
Source: PA