Riley, who grew up in Lytham, Lancashire, joined Manchester United’s academy at six. He progressed through the ranks and featured for the under-18s alongside Marcus Rashford, Scotland midfielder Scott McTominay (now at Napoli), and England goalkeeper Dean Henderson (now at Crystal Palace).
By 19, Riley was a regular with the under-21s, and in February 2016 he and the then 18-year-old Rashford were handed their senior breakthroughs by Louis van Gaal. After coming off the bench in a 3-0 FA Cup fifth-round win at Shrewsbury Town three days earlier, Riley was named in the starting XI for the Europa League last-32 second leg against Midtjylland.
United trailed 2-1 from the first leg in Denmark and were hit by injuries to key players, including Wayne Rooney, David de Gea, Antonio Valencia and Chris Smalling. In the team meeting the day before the match, Riley was stunned to see his name listed among established stars like Michael Carrick, Daley Blind, Juan Mata, Jesse Lingard and Memphis Depay.
With his mother, Derren, and sister, Sophie, among the 58,609 at Old Trafford, Riley started and played 79 minutes, earning a standing ovation when he made way for Marcos Rojo, who was returning from a dislocated shoulder. United led 3-1 on the night (4-3 on aggregate) at the time and went on to add two late goals to book a last-16 tie with Liverpool. Despite playing well, Riley sensed it might be his final first-team appearance with Rojo and Luke Shaw nearing fitness.
His instinct proved right. While Rashford featured frequently for the remainder of the season, including in United’s FA Cup final win over Crystal Palace, Riley did not play for the senior side again. He continued training with the first team after Van Gaal’s departure and Jose Mourinho’s arrival in May 2016, and he captained the under-23s.
Injuries began to take their toll in 2017. A hamstring problem delayed a loan to Sheffield United, and a subsequent dislocated shoulder cut that spell short. Riley’s 15-year stay at United ended on 25 May 2018. As former youth teammate Rashford prepared for the World Cup with England, Riley signed a two-year deal with League One side Bradford City.