 After a trial, Nicholson signed a two-and-a-half-year contract with League One club Peterborough United on 24 December 2015, at which point he gave up his former job as a carer.He made his Football League debut on 20 February 2016, coming on as a half-time substitute for Harry Toffolo in a 3–0 defeat to Millwall at The Den.He was loaned to National League North club Nuneaton Town on 4 August 2016 for the season, but was recalled in March 2017 because his parent club wanted to assess him.