Mackin made his first appearance of 2010–11 in the opening match, a 2–1 home defeat to Kidderminster on 14 August 2010, and was substituted in the 38th minute due to an injury and Foyle said "It looks a bad one and he might need a scan". The scan revealed no knee ligament damage had occurred and it was estimated he would be injured for a month. He returned to training in November 2010, having been out of the team injured for almost three months, returning as an 87th-minute substitute in a 3–0 home win over League Two team Rotherham United in an FA Cup first round replay on 17 November. He scored at home for the first time for York with the 85th-minute winner against Forest Green on 22 January 2011, the goal being a drilled shot into the bottom corner. Mackin finished the season with 13 appearances and 1 goal before being released by York in June 2011 after being told he could find another club.