Klopp told Goal and Spox: "It sounds a bit strange, but we could not afford it, we have already spent the cash that we got for him.
The German added: "We were reluctant to hand him over, but Barcelona forced us with money, so to speak.
"The move makes sense for both sides. He's a super player and a great boy. He is a world-class footballer who can change games in the right environment."