The German stopper broke down in tears and made apologetic gestures to his side's supporters in the stands after the match, which Hamann - a 2005 Champions League winner with Liverpool - did not agree with.
"My sympathy with Karius is limited," he told Sport Bild. "We don't have to discuss that he decided the final with his two mistakes. Something like that can also happen to a professional footballer. But what I didn't like was his behaviour afterwards.
"To publicly show his suffering after the final whistle was just as unnecessary as his tearful asking for forgiveness from the Reds fans. Liverpool fans forgive their stars just as well as any other, the anthem 'You'll Never Walk Alone' is part of life out at the club. With one exception: when your ego doesn't match your performance.
"Karius drives through Liverpool with the personalised number plates 'LK1' and makes waves in the city whenever he steps out. That is something Cristiano Ronaldo can pull off in Madrid, because he has won the Champions League five times.
"Someone like Karius has not achieved anything yet in his career and should be happy to have been given the chance by Klopp at a world-class club."