Horkaš started playing football at his hometown club Segesta, before joining Dinamo Zagreb's youth academy in 2011. He made his professional debut against Imotski on 11 December 2016 at the age of 17.[1]
In January 2020, he was loaned to Bosnian team Zrinjski Mostar until the end of season. In June, his loan was extended for additional six months.[2]
In October, he was sent on a season-long loan to Varaždin.[3]
In January 2022, Horkaš was loaned to Posušje for the remainder of campaign.[4]