Combo help for mortal kombat 9?

when i go into practice mode to study the moves theres some problems i have with the combos. i use quan chi. and he has a move called sky drop which is left right then x. that works fine. but i wanna do sky drop + kick. which is left right x + R2 every time i do it. it don't work. even if i have a super bar. what am i doing wrong?