Klopp has suggested that perhaps Real president Florentino Perez needed the money after buying Gareth Bale for £84m.
"I do not care which player will play against us in the UEFA Champions League," Sky Sports News quotes Klopp as saying. "But Mesut is a football grenade. No-one really knows why he was sold. Maybe Real Madrid needed the money?
"Real Madrid chairman Florentino Perez wanted to have Gareth Bale, of course, and he paid £84m.
"Perez once even bought Hochtief [a German construction company]. Maybe he just doesn't know in the mornings what he is about to do with his money when the evening comes."
The fee to take Ozil to Arsenal was £42.5m.