The 29-year-old has been on loan at Glanford Park from the Silkmen, and has signed a deal until the end of the season.
United have the option of extending it for a further 12 months in the summer.
Iron seal MacKenzie signing
The 29-year-old has been on loan at Glanford Park from the Silkmen, and has signed a deal until the end of the season.
United have the option of extending it for a further 12 months in the summer.