The left back was signed in 2014, but failed to show the necessary quality or consistency to establish himself as a mainstay in the position.
He was not able to show Klopp that he was good enough for the first time, which led to his eventual sale.
Moreno has now lifted the lid on that relationship.
"After the Europa League Final (2016) I spent the year on the bench. Then I thought of leaving," the Spaniard told local paper El Periodico Mediterraneo.
"Klopp told me if I got something really good and he didn't need me, to talk, but in the end he convinced me to stay.
"And the first day came and I started playing, Premier League, Champions League, always starting.
"[Then-Spain coach Julen] Lopetegui even called me, Lopetegui for the national team.
"But I was injured in December and after I recovered, I no longer played.
"Klopp no longer gave me opportunities. He's a very good coach, but he decides to go forward with his 13 or 14 players and that works."