 The same happened at the start of the 1963–64 season, and although United manager Matt Busby offered to extend McMillan's contract by a year, the Ulsterman was desperate for first team football and he was sold to Wrexham for £8,000 on Christmas Eve 1963.McMillan scored a commendable seven goals from 20 appearances in his first season with Wrexham, but it was not enough to prevent the Welsh side from being relegated to the Fourth Division.In five seasons with Wrexham, McMillan scored a total of 52 goals, including a season's best of 18 in 1966–67, and was just one appearance short of 150 for the Red Dragons before being sold to Southend United for £6,000 in 1967.