 He made his 200th career appearance for Sutton in September 2015 and was part of the team which won the National League South title.On 4 December 2016, Downer appeared in The Non-League Paper's team of the day alongside teammate Roarie Deacon and manager Paul Doswell following an impressive performance in Sutton's 2–1 victory over League Two side Cheltenham Town in the 2nd round of the FA Cup on 3 December.Downer appeared in every round of Sutton's historic run to the 5th round of the FA Cup for the first time ever, including a 3–1 victory over League One team and local rivals AFC Wimbledon on 17 January 2017, a 1–0 victory over Championship team Leeds United on 29 January and a 0–2 defeat to Premier League Arsenal on 20 February.