Boateng: Klopp comments made me angry

Boateng spent a stint on loan at Dortmund in the 2008-09 season and impressed, before continuing his career at Portsmouth and Milan.

The Ghana international caused a stir when he signed for Dortmund's arch-rivals Schalke last week, and Klopp made comments in jest about the 26-year-old.

Klopp said: "I'm really surprised. I sent him a text message saying 'Why Schalke' with eight question marks, but I didn't hear back from him.

"He was a good lad, up until this morning."

Boateng played a key role in Schalke's 2-0 Bundesliga win over Bayer Leverkusen on Saturday, as a result that snapped a three-game winless run in the German top flight.

And Schalke's new star man has said that he was unhappy with Klopp's comments.

"Many people thought it was funny, but I didn't," he told Sport-Bild.

"Even if 'Kloppo' and I have a good relationship, he's not going to hear me say a bad word about him, but this press conference surprised me."