[1] Riis was promoted to Midtjylland's first-team squad in the summer 2016 at the age of 19, signing a five-year professional contract on 14 June 2016.
[5] After unexpectedly earning a spot to represent the Danish under-21s in early April 2017, Riis encountered a setback when he sustained a knee injury, sidelining him for 4 to 5 weeks.
[2] Riis played the first eight games of the 2022–23 season, before suffering a torn meniscus in early September 2022, which required surgery and an injury break for the rest of 2022.
[13] On 30 December 2023, Riis confirmed that at the age of 26, he had been forced to end his professional football career as his 'body could no longer keep up' due to numerous injuries.
[14] After retiring, Riis returned to his former club, FC Midtjylland, where he joined the academy staff, functioning as an individual coach.