In 2008, Gregoritsch began his career at Kapfenberger SV's youth teams and was promoted to the Austrian Bundesliga team in January 2010. He made his debut on 14 April 2010 against Austria Wien and scored his first league goal less than three minutes after coming on as an 82nd-minute substitute. This made him the youngest goalscorer in the history of the Austrian Bundesliga with only 15 years and 361 days.