Sterling returns to Anfield on Sunday with Manchester City.
Klopp said, "He was always a big threat and looks like improving and improving and improving - that's good for Manchester City and England.
"He was already a big talent at that time - a fantastic football player, I can't say anything bad about him.
"Just outstanding, I heard Pep saying if he starts to finish all the situations he has, then it will be really, he will be there.
"He is a threat but not the only one unfortunately, that's the problem we have."