Hamann was in the 2002 team, a beaten finalist in Yokohama as Rudi Vollerâ€™s side came up against the brilliance of the Brazilian Ronaldo.
He told the Daily Mail: "Iâ€™m still cautious about Germany because in the previous three tournaments they had better teams than this one and didnâ€™t win any of them.
"Bastian Schweinsteiger has had a lot of problems with injuries and if he doesnâ€™t perform then Germany cannot win the World Cup - it really is as simple as that.
"If you look at the bench they have no experience. They have a team with six or seven players with less than five caps each.
"This is a difficult tournament for Germany to win because their route to the final is probably France, then Brazil, then Argentina or Holland in the Maracana.
"It is seven games of high intensity and the players have to perform at their very best.
"Look at Neymar - he is 22 years old and everyone in Brazil is putting pressure on him to win the World Cup and he has to handle that after a very difficult first season with Barcelona."
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