Germany great Jurgen Klinsmann's Californian-born son Jonathan is "too American" and must work harder to make an impact in the Bundesliga, the Hertha Berlin goalkeeper's coach said on Wednesday.

The 20-year-old Klinsmann, whose father won the 1990 World Cup as a striker and coached Germany at the 2006 tournament, joined Hertha last July.

Raised in the United States, the club's third choice keeper suggested at a press conference on Tuesday that his laid back approach helped him to be "less nervous" on the pitch.

But Hertha's goalkeeping coach Zsolt Petry took an alternative view.

"These last two or three months haven't been good. We aren't happy with his progress, he's still a little too American," Petry told the domestic media.

"He has still not fully taken on board the German virtues like concentrating on hard work. In professional football, if you don't have that, you are lost."

Klinsmann's playing time has been confined to the reserves, with his only first team appearance coming when he saved a penalty in a Europa League tie against Ostersund.

Klinsmann junior nevertheless has high hopes, declaring: "My long term aim is to become number one here in Berlin.

"I want one day that when people say Klinsmann, people think of Jurgen and of Jonathan."

The younger Klinsmann played for the United States at last year's Under-20 World Cup in South Korea.