Klopp has refused to deny he is keen to sign the USA international.
"He has a contract at Dortmund, no? That's the first problem," said Klopp.
"I like Christian, I've known him since he was a kid. He's still not really old, he's a fantastic player, and it's deserved people think highly of him in America. In Germany it's the same.
"If he wants to play in England or whatever one day then for sure he has the chance to do so but he's at a really good club for his development at this moment. It's really good to be at a club where they know him already."