Simon joined Oxford for the second time in June 2016, from Blackburn Rovers. Having started his career with Huddersfield, Simon joined the U’s from the Terriers in June 2010 but was unable to break into the first team. At the end of the season he was released and signed for Halifax Town. After one season Michael Appleton signed him for Portsmouth, and in May 2013 Appleton, who was then manager of Blackburn, signed him for Rovers.

Simon, who has been capped for England at under-18 and under-19 levels, won both the Supporters’ Player of the Year and the Players’ Player of the Year awards for 2016/17. He signed a new three-year contract with United in May 2018 and another three-year deal in April 2021. Made his 250th Oxford appearance against Peterborough on 22nd October 2022.