[1][2] Riel began his senior career in HIK before moving the Faroese club B36 Tórshavn in 2009, where he spent six months.
He subsequently bounced around in the lower divisions of Danish football, playing for BSV, Fremad Amager, Vendsyssel FF,[3] and FC Helsingør.
Riel experienced his breakthrough in Helsingør, and his 17 goals in 32 appearances in the 2016–17 season in the second tier helped the club secure promotion to the Danish Superliga after two decisive play-off matches against Viborg FF in June 2017.
[4] In the following season, Riel scored 4 goals in 7 appearances in the Superliga for Helsingør, before signing with AGF on deadline-day of the 2017 summer transfer window.
[16] One day after leaving Lyngby, it was confirmed that Riel had joined Danish 2nd Division club Boldklubben Frem.