 After initially suffering from injury, he made his Milton Keynes Dons' debut in the second round of the League Cup, in a 3–0 win over Charlton Athletic.A week later, on 25 August 2018, Cargill made his first start for the club, in a 3–0 win over Exeter City.Three days later, on 28 August 2018, he played against his former club, Bournemouth, in the second round of the League Cup and the match ended with Milton Keynes Dons losing 3–0.