The Steelmen's player-coach and academy director has three games to save the club from suffering successive relegations after Saturday's 2-0 defeat at home to Whitby Town in the EVO-STIK NPL's top flight cost Mills his post.
Appointed back in October after leaving his post as assistant manager at King's Lynn Town, the FA Trophy winner with Stevenage and former Rushden & Diamonds star was thanked for his services in a short statement confirming his departure from the fourth from bottom Steelmen.
A spokesman said: "We would like to thank Gary for his hard work since joining the club and wish him the best in his future career."
Scot Kinniburgh can forget about the club's relegation fight in his first game at the helm with the Steelmen preparing to meet Kettering Town at Northampton's Sixfields Stadium on Tuesday night in the final of the Northamptonshire Senior Cup.
With his new charges without a league win in their last five outings and three points from safety, the real work for Kinniburgh starts on Saturday when the Steelmen head to Stafford Rangers in search of a victory with time running to avoid a repeat of last year's relegation from the National League.
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